☠ WARNING ☠

Skydiving is an inherently risky activity that can lead to injury or death. All skydiving equipment is subject to failure. Failure to follow instructions, warnings, and operating procedures could imperil you and others. Every skydiver is solely responsible for his or her safety on each skydive he or she makes. SirenAlti is an audible altimeter that communicates entirely through synthesized tones—beeps and sirens. Audible altimeters use high sound pressure levels in order to cut through noise and can cause hearing damage; for this reason, Freefall Data Systems LLC recommends wearing earplugs when using any type of audible altimeter. Altimeters are subject to error and malfunction and should only be used as a secondary indication of altitude—second to a visual ascertainment. It is possible that any altimeter can read higher than the distance you actually are above ground level. Failure to maintain visual altitude awareness regardless of altimeter readings can lead to serious injury or death. The default settings on the device are merely suggestions; skydivers should set the altimeter for their own specific use case. Many factors can compromise the accuracy of a barometric altimeter reading, including but not limited to: body position, position relative to other skydivers or objects, altimeter placement, temperature, and malfunction. Additionally, just because two altimeters are in sync during ascent, this does not mean they will be in sync during freefall or under canopy, as barometric altimeters are more greatly affected by wakes (burbles) at high speeds than at low speeds. Audition and understand each alarm you assign before jumping the altimeter, and confirm the selected preset on the ground before every jump. This altimeter contains a lithium battery; do not use it if the case is damaged in any way. Stop use immediately if the device becomes excessively hot, begins to swell, or emits an odor.

Regarding Tactical Mode: SirenAlti includes an optional, per-preset Tactical Mode intended for specialized operations (e.g. smokejumping, military static-line jumping, and HAHO). Tactical Mode should in no case be used for normal skydiving operations, as the altimeter functions entirely differently. See section 4.8 below for a full description.

LIMITS OF LIABILITY

This product was manufactured for skydiving only. By using this product, you accept full responsibility for its use and agree that you are solely responsible for each skydive you make as well as your safety and that Freefall Data Systems LLC will not be held legally responsible for any malfunction whatsoever that this product may have, whether good or defective.

1.1 SirenAlti description

SirenAlti is a beeping audible altimeter with two speakers rather than one. It communicates entirely through synthesized tones—beeps and sirens. The second speaker is not redundancy: it makes stereo alarms possible, and it allows the two speakers to be offset slightly in frequency so that an alarm shimmers rather than sounds flat (section 4.1). The result is a far larger and more distinguishable set of alarms than a single-speaker audible can produce.

The altimeter holds five presets, each with its own alarms, volumes, landing-zone offset, and freefall threshold. Presets are built in the free Bluetooth^® FDS Altis app for iOS and Android, and then selected on the device itself using its buttons—you do not need your phone in order to use the device. SirenAlti is always on, adjusts automatically to local elevation, and logs your jumps for syncing to FDS Logbook (section 5.1).

It is a barometric altimeter and contains no GPS. It has a rechargeable lithium battery with a life of approximately 80 jumps or three months, and charges via USB-C. SirenAlti can be used from −5,900 to 30,000 feet MSL.

1.2 The device, buttons, and indicators

On the side of the altimeter there is a USB-C port, which serves two purposes: charging (section 6.2) and firmware updates (section 7.1). Beside it is a small window containing two indicator LEDs—a red LED that is lit while the altimeter is charging and goes out when charging is complete, and a blue LED that indicates Bluetooth^® activity (section 3.1).

Adjacent to the LED window is the vent for the pressure sensor. Do not cover or obstruct this vent, as doing so will affect the accuracy of the altimeter's readings. On the opposite side are the two speakers, which should generally face your ear.

There are two buttons:

• The settings button (marked with a gear) selects the current preset. See section 4.7.
• The Bluetooth^® button (BLE) puts the altimeter into Bluetooth^® mode for use with the app. See section 3.1.

Pressed together, the two buttons give access to two further functions: the current battery level (section 6.3) and Sleep Mode (section 6.5).

Next to the BLE button is a small hole giving access to the reset button, which requires a paperclip or something similar to activate. A single click of the reset button is the first step in troubleshooting (section 8.1); a fast double click puts the altimeter into firmware-update mode (section 7.1).

2.1 Altimeter installation

Most skydiving helmets include a pocket for an audible altimeter, and SirenAlti is small enough to fit comfortably in them. Place the altimeter in the pocket with the speakers facing your ear.

Check the selected preset before you put your helmet on. Hold down the settings button and count the beeps; the number of beeps is the currently selected preset (section 4.7).

SirenAlti is waterproof to a depth of three feet for thirty minutes, so a pond swoop or a day of rain should not present a problem. Dry the device afterwards—setting it in front of a fan for a period of time is sufficient.

3.1 Downloading and connecting to the app

SirenAlti is configured with the free FDS Altis app, available for iOS and Android. The two versions are very similar; where they differ is noted in this manual. On opening the app you will be asked to read the warning and limits of liability agreement.

To connect, put the altimeter into Bluetooth^® mode by holding down the BLE button until you hear the Bluetooth^® chime. The blue LED then begins flashing. Select the device in the app; once connected, the blue LED is lit steadily rather than flashing.

The app presents three sections: Settings, Data Syncing, and Info. If Data Syncing appears greyed out after you connect, it is because you are not signed in to an FDS Logbook account; you must create one first. Signing in and out is done on the device selection screen at the top. Once you are signed in, Data Syncing is no longer greyed out.

Bluetooth^® mode times out automatically. You can also exit it by holding down the BLE button again until you hear the exiting chime, or by pressing Disconnect in the app. The blue LED goes out, and after a brief moment the buttons resume their normal functions.

The Info screen at the bottom of the app shows, in order: the device serial number (a five-digit number, which doubles as a discount code for a free year of FDS Logbook), the current battery percentage, the number of jumps currently held in flash memory, and the current firmware version.

4.1 Main settings

Main settings apply to all five presets. They are found at the top of the Settings screen.

• Metric mode — switches the altimeter and app to metric units.
• Log jumps — disables logging, which is useful if you loan the device out. With logging switched off the altimeter will neither log the jump nor increment the next jump number.
• Next jump number — setting this correctly is one of the first things to do with a new altimeter.
• Center frequency — raises or lowers the pitch of every sound globally. The factory setting in the middle of the range is chosen to maximize the effectiveness of the alarms in psychoacoustic terms, so we recommend leaving it alone unless you have trouble hearing the device, in which case it is worth experimenting.
• Simple alarms beating — unique to SirenAlti. By default the two speakers sound in unison; raising this value sets them slightly apart in frequency, introducing a shimmering, beating quality that can increase the salience of certain alarms. This only applies to the Simple category (section 4.4).
• Copy preset — enter the preset you would like to copy from and the preset you would like to copy it to, then press Go. Useful for building a variation on a preset you already use.

4.2 Presets: general settings

All five presets are identical when the altimeter is new. At the top of each preset are the General settings.

• Landing-zone offset — enter a positive number if your landing zone is higher than your take-off point, a negative number if it is lower. For example, landing 300 feet higher than take-off is entered as 300; landing 200 feet lower is entered as −200. The app will confirm in words what you have told the altimeter to do—read the confirmation. FDS has chosen to indicate ascent alarms with an LZ offset according to takeoff altitude, assuming jumpers are closer to the airport in an emergency. Upon exiting the aircraft, the landing zone offset takes effect.
• Custom freefall threshold — the vertical speed at or above which the altimeter considers you to be in freefall. The default is 80 mph, which is a good value for skydiving without a wingsuit. A wingsuiter flying a moderately sized suit might set around 40 mph and work down from there; XRW may require values as low as 20 mph to distinguish freefall from canopy flight. A workaround: Wingsuiters can also just set the value of the freefall threshold to something extremely high like 300 mph and then only use canopy alarms (this of course has the disadvantage of no differentiation between freefall and canopy).
• Force canopy below — below the altitude set here, the altimeter gives canopy indications only, regardless of speed. This is useful and actually highly recommended for swoopers, who may exceed freefall speeds under canopy at altitudes where freefall would not be safe. Most jumpers should leave this alone.
• Volume levels — separate volume levels for each of the three phases of the skydive: ascent, freefall, and canopy.
• Tactical Mode — an optional, per-preset mode for specialized operations. See section 4.8.

Regarding volumes: the defaults are reasonable starting values, but the correct settings depend on your helmet, your ears, and your discipline. Wind noise in freefall is considerable, and aircraft noise on the ride up can be as well. You can audition levels in the app, but the only reliable method is to jump the altimeter a few times and dial the values in over a series of jumps. Freefall Data Systems recommends wearing earplugs with any audible altimeter, and for hearing protection while skydiving generally.

4.3 Presets: alarms

Each preset carries its own alarms, organized under the three phases of the skydive: Ascent, Freefall, and Canopy. There is no limit to the number of alarms you may place in a preset.

How an alarm is entered depends on the phase:

• Ascent — alarms are single thresholds. Enter the altitude and press Insert; the alarm sounds for four seconds once as you pass that altitude on the way up.
• Freefall and canopy — alarms are given an altitude range, for example 6,000 to 4,500 feet, and the alarm sounds across that range.

Alarms can be auditioned in the app before you commit to them, and removed at any time—on iOS by swiping left, on Android by holding down on the alarm for a moment.

A note on the High and Low labels. Sounds labeled High use higher frequencies, which cut through high wind noise more easily; these are best suited to freefall. Sounds labeled Low are better suited to the quieter phases of ascent and canopy flight. The default preset follows this convention, and it is generally worth following in your own designs.

4.4 The sound library

SirenAlti carries 90 sounds—more possibilities than any other beeping audible altimeter currently known to us. They fall into three categories:

• Simple — both speakers do the same thing, though they may be detuned from one another by the Simple alarms beating setting described in section 4.1.
• Dual — the two speakers do different things, producing a large variety of stereo alarms that a single-speaker audible cannot make at all.
• Musical — short musical figures. These can be every bit as effective as the other categories in the right context, and add a little humor and levity to a jump.

All 90 sounds can be auditioned in the app (section 4.6), and can also be heard in a browser at freefalldatasystems.com/sirenalti_sounds. Note that you will need stereo speakers or headphones to hear them accurately, since the altimeter itself is a stereo device.

4.5 Static and dynamic alarms

Sounds marked with a triangle (▲) are what we call dynamic alarms; the rest are static. A static alarm repeats unchanged for as long as it is sounding. A dynamic alarm changes across the altitude range you assign it—in technical terms it is a sonification of altitude. A dynamic alarm might accelerate as you descend toward a threshold, so that the sound itself tells you how fast you are approaching it.

If you plan to deploy at 4,500 feet, you might consider assigning an accelerating dynamic alarm across the range above it, and the alarm will stretch or compress to cover exactly that range at your actual descent rate. Dynamic alarms can be useful for canopy flight as well, where they are excellent for gauging closing rate.

It is worth putting a lot of thought into alarm design as good design can help keep you safer and more altitude aware. The defaults described in section 4.9 are solid, proven starting recommendations rather than the limit of what the altimeter can do.

4.6 Presets: simulations

The Simulation screen does two things. First, it is a sampler: you can audition every sound in SirenAlti, setting the volume at the top and the number of seconds you would like to hear each sound for.

Second, it will simulate the preset you are currently in—the simulation always pertains to the preset from which you opened it. Give it a descent rate and it begins at your first alarm and plays the preset through, which is a very good way to get an idea of what your alarms will actually sound like in sequence before jumping.

4.7 Selecting presets

Presets are built in the app but selected on the altimeter, so you do not need your phone with you. Selection is done entirely with the settings button, and the altimeter tells you your preset number in beeps:

• To check the current preset — hold down the settings button and count the beeps. One beep is preset 1, two beeps is preset 2, and so on. If it has been a while since you last touched the altimeter, a press of the settings button will also report the current preset.
• To change the preset — keep the button held down and the altimeter cycles through the presets. Release when you reach the one you want.

Confirm your preset on the ground or in the aircraft after setting or when unsure (e.g. it has been a while since jumping it).

4.8 Tactical Mode

WARNING: Tactical Mode should in no case be used for normal skydiving operations, as the altimeter functions entirely differently. Tactical Mode is an optional, per-preset capability intended for specialized operations such as smokejumping and military static-line jumping, where unusual flight paths are followed, exits sometimes occur far lower than in sport skydiving, and the device must be ready instantly. It is enabled per preset on the General settings screen (section 4.2).

Because the altimeter's behavior changes fundamentally on a preset with Tactical Mode active—including a significant impact on battery life—the app asks you to confirm when you switch it on.

A separate instructional video covering Tactical Mode in detail is available; see the video description for the link.

4.9 Default settings

All five presets ship identically configured, with Tactical Mode off. The default alarms are as follows.

• Ascent — a gear-check alarm at 12,000 feet and a seatbelts alarm at 1,500 feet, both Low Slow Beeps.
• Freefall — High Accelerating Beeps from 5,500 to 4,000 feet (gauging closing rate with a dynamic alarm), then Opposing Rising/Falling Siren (Medium) from 4,000 to 3,000 feet and Opposing Rising/Falling Siren (Fast) from 3,000 to 2,000 feet. The alarms cut out below 2,000 feet, so their absence is itself an indication.
• Canopy — Low Fast Beeps beginning at 1,000 feet, Low Medium Beeps at 600 feet, and Low Flatline at 300 feet, corresponding to a standard downwind, base, and final.

Note the use of High sounds in freefall and Low sounds in ascent and canopy, per section 4.3. These defaults are proven recommendations, but they are only recommendations—you should set the altimeter for your own use case, your own discipline, and your own landing pattern.

5.1 Data Syncing

SirenAlti is a logging altimeter. Jumps are stored in flash memory on the device and synced to FDS Logbook through the FDS Altis app.

The Data Syncing screen is also where you select the gear you are jumping, your location, and the aircraft, so that these are attached to the jumps as they upload. If these lists appear empty, it is because you have not yet set them up in FDS Logbook—you must first tell it what you jump and what you jump out of. When the altimeter is holding jumps, the screen indicates as much, and you can download them; they appear in FDS Logbook in real time as they upload.

Sync often. Letting jumps accumulate in flash memory—more than a hundred, say—makes the transfer considerably more of a chore than it needs to be. It happens more often also that the jump numbers or dates are off when they accumulate.

FDS Logbook is approved by the United States Parachute Association, so the FDS Altis app can also be used to get jumps signed off conveniently. There is a separate instructional video covering FDS Logbook, which is worth watching—its features go well beyond the scope of this manual.

6.1 Battery life

SirenAlti has a rechargeable lithium battery giving a life of approximately 80 jumps, or about three months. The altimeter is always on; there is no power switch. If you expect to leave it unused for an extended period (winter breaks), put it into Sleep Mode (section 6.5).

A low-battery warning sounds at 1,000 feet when the battery is running low.

6.2 Charging and maintaining the battery

Charge the altimeter by plugging it into a USB-C cable. The red LED in the indicator window is lit while charging and goes out when the altimeter is fully charged. A USB-C cable is included with the altimeter, and all cables sold or supplied by Freefall Data Systems are data cables suitable for both charging and firmware updates.

The permissible charging temperature range is 0° to +50° C (32° to 122° F). Do not charge the device outside this range.

6.3 Checking battery status

There are two ways to check the battery.

• On the altimeter — hold down both buttons together. The altimeter reports the battery level as a number of beeps from 1 to 10: ten beeps is full, five beeps is approximately 50 percent, and so on.
• In the app — the Info screen shows the battery as a percentage (section 3.1).

6.4 Checking firmware

The current firmware version is shown at the bottom of the Info screen in the FDS Altis app (section 3.1). This is also how you confirm that a firmware update has been applied successfully (section 7.1).

6.5 Sleep Mode

Sleep Mode is also reached by holding down both buttons. Hold down both buttons together and the altimeter first reports the battery level in beeps (section 6.3), and if you continue holding, it enters Sleep Mode, which is confirmed by a distinct sound (a falling pitch).

The altimeter does not register altitude while it is in Sleep Mode. It is intended for storage and shipping, not for use. Waking it is simply a matter of pressing a button (you will hear a rising pitch upon the device waking).

7.1 Firmware updates

Firmware is updated by dragging a file onto the altimeter as though it were a USB drive.

1. 1. Download the latest firmware file from freefalldatasystems.com/sirenalti_firmware.
2. 2. Plug the altimeter into a computer using a data USB cable. Not all USB cables carry data; all cables we sell or include with altimeters do.
3. 3. Using a paperclip, give the reset button between the two buttons a quick double click. It is important that the double click is fast.
4. 4. The altimeter appears on the computer as a USB drive named FDS ALTI. Drag the new firmware file onto it.
5. 5. You will often see a failure message from the computer, because the altimeter disconnects itself once the update is applied. This is normal. Confirm the update by connecting to the FDS Altis app and checking the firmware version under Info (section 6.4).

8.1 Troubleshooting

If the altimeter is behaving unexpectedly, the first step is a single click of the reset button, reached through the small hole next to the BLE button with a paperclip. This restarts the device and re-zeros the altitude. It does not erase your settings or your logged jumps.

If a computer does not recognize the altimeter during a firmware update and you are certain you are using a data cable, try a different computer, and try a different cable in case that is the weak link. Security settings and other local conditions sometimes prevent it from working for reasons that are not always apparent. It is usually not worth spending much time on a machine that will not cooperate, as the procedure works on the large majority of computers.

If the altimeter does not respond at all, check that it is not in Sleep Mode (section 6.5) and that the battery is not depleted (section 6.3).

If you have any questions, feel free to contact us by email or telephone.

8.2 Restoring default settings and erasing jumps

Restoring default settings and erasing all jumps are each performed by holding a button down through a reset (a single click of the reset button, section 8.1). In both cases the blue LED flashes while a five-second hold is counted, and the altimeter plays a rising high-pitched sweep once the action completes. Restoring defaults and erasing jumps cannot be undone.

• Restore default settings: hold down the preset button and, while keeping it held, press and release the reset button; continue holding the preset button for about five seconds, until you hear the sweep. All five presets and the Main settings are rewritten to the factory defaults.
• Erase all jumps: hold down the Bluetooth button and, while keeping it held, press and release the reset button; continue holding for about five seconds, until you hear the sweep. All logged jumps are deleted and the jump counter is reset to 1.
• Do both at once: hold down both buttons through the reset and keep holding until you hear the sweep.

If you release the button before the five seconds are up, no action is taken and the altimeter simply starts up normally. Do not hold down either button while double-clicking reset for a firmware update.

9.1 Technical specifications

• Dimensions: 42.0 × 35.0 × 12.6 mm (1.65 × 1.38 × 0.50 in)
• Weight: 30.3 g (1.07 oz)
• Case material: 6061 aluminum
• Anodizing type: MIL-A-8625F Type II
• Water ingress protection: IP67
• Battery: rechargeable lithium ion 3.7V 165mAh
• Speakers: two, piezo
• Peak alarm output volume: 100 dBA @ 10 cm
• Audio types: synthesized tone alarms
• Sound library: 90 sounds in three categories (Simple, Dual, Musical)
• Presets: five, selectable on the device
• Operating temperature range: −40° to +65° C (−40° to 149° F)
• Operating altitude: −1,800 to 9,160 m MSL (−5,900 to 30,000 ft)
• Relative altitude accuracy: ±0.75 m (2.5 ft)
• Sample rate: 25 Hz
• Permissible charging temperature range: 0° to +50° C (32° to 122° F)
• USB connector: USB-C
• Radio capabilities: Bluetooth Low Energy
• Made in the USA