Consumer wearable fall detection is not magic. It is pattern matching on accelerometer data, and understanding what that means helps you set realistic expectations.
What an accelerometer measures
An accelerometer measures the rate of change of velocity — acceleration — in three axes. When you fall, there is a characteristic sequence: a period of free-fall (near-zero acceleration as gravity acts uniformly), followed by a high-magnitude impact as you hit the ground, followed by a period of low movement as you lie still.
Fall detection algorithms look for this sequence. The specific thresholds — how large the impact needs to be, how long the stillness needs to last — vary by implementation and are tunable.
Where it works well
Hard falls onto a hard surface, where the wearer loses consciousness or is unable to get up, produce a clear signature. These are the cases where detection is most reliable and most valuable.
Where it fails
Slow falls — where the person lowers themselves to the floor gradually due to dizziness or weakness — often do not produce the expected impact signature. The free-fall phase is absent or very short. These are also the falls most likely to indicate a serious medical event, which makes this a significant limitation.
Falls onto soft surfaces (carpet, a bed) produce a lower-magnitude impact and may not cross the detection threshold. Falls where the person catches themselves partially may not produce enough stillness to confirm the event.
Conversely, vigorous exercise, sitting down heavily, or dropping the device can all produce signatures that look like falls. This is why Guardian uses a two-stage confirmation process: the wearer gets a check-in prompt before anyone else is alerted.
The honest summary
Fall detection on a consumer wearable is a useful early-warning layer, not a guarantee. It catches a meaningful proportion of hard falls. It misses slow falls and falls on soft surfaces. It generates false alarms. The value is in the combination: detection plus a human circle who can respond, plus a clear record of what happened.