Man down detection explained: how it works, where it fails, and what covers the gap
By the SafetyEvo team · · 6 min read
Man down detection, also called fall detection, is an automatic alarm raised when a device decides the worker may be unable to call for help: it has detected a fall, a hard impact, the device lying flat, or no movement for a set time. It exists because an SOS button is useless to someone who is unconscious. It is a valuable control for a small set of tasks and an unreliable one for most, and this guide explains both, including why SafetyEvo does not offer it today.
How detection works
Every modern device and phone has an accelerometer that measures movement in three directions, and most have a gyroscope that measures rotation. Man down software looks for patterns in that data. Impact detection looks for a sharp spike followed by stillness. Tilt detection looks for the device lying at an angle for longer than a set time, on the assumption that a badge or fob worn upright has fallen with its wearer. No-motion detection looks for an absence of movement over a window the employer sets, often two to five minutes. When a pattern matches, the device sounds a pre-alarm, usually a loud tone and vibration for 15 to 60 seconds, so a worker who is fine can cancel it. If nobody cancels, the alarm is sent with the location to the responders or the monitoring centre.
Why it false alarms, and why that matters
The detector cannot tell a fall from a phone dropped on a seat, a device set down on a bench from a worker lying still, or a worker sitting through a long meeting from one who has collapsed. Every false alarm costs responder time and trust, and after enough of them the pre-alarm gets cancelled without a glance and real alarms get the same treatment. Employers who have run man down on phones report the same thing: the setting that avoids false alarms is the one that misses real falls. Wearables fixed to the body do better because they move with the body, but even they need the sensitivity tuned per role.
When it is worth having
- Work at height alone, where a fall is the main hazard. HSE’s work at height guidance applies, and the first question is whether the task should be done alone at all.
- Confined spaces, where gas or lack of oxygen can cause collapse without warning. Confined space rules in practice require more than one person and a rescue plan; a man down device is a supplement, not the control.
- Working alone with machinery, animals or hazardous substances.
- Workers with a medical condition that could cause sudden collapse, where the risk assessment has judged lone working acceptable with this control.
- Hostile environments where a worker may be attacked and unable to press a button.
What covers the gap when you do not have it
The risk man down addresses is "something happened and nobody noticed". Two controls that do not depend on sensors cover most of that risk for most lone workers. A check-in timer, set before a risky task, raises an alert on the worker’s behalf if they do not confirm they are safe before it runs out, and because the timer runs on the server it works even if the phone is broken in the fall. Silent phone detection raises an alert when a phone that should be reporting stops, which catches a phone destroyed, a battery flat or an app closed. Add a welfare check from the office at agreed points in a shift and you have a schedule of moments when someone would notice, which for a 30 minute timer means at most 30 minutes before the alarm, with almost no false alarms.
For the tasks in the list above, that is not enough, and the answer is a wearable device with fall detection, or two people. SafetyEvo will say so rather than sell you a phone sensor that does not work in a pocket.
Questions to ask any vendor about man down
- Is the detection on a wearable or on a phone? Where on the body is it designed to be worn?
- What triggers it: impact, tilt, no motion, or all three? Can each be switched off per role?
- How long is the pre-alarm, and can the worker cancel it with gloves on?
- What is the false alarm rate in a role like ours, and can we see it in a trial?
- What happens after the alarm: who is told, by what channel, and what do they do?
- Is the alarm logged with the sensor data, so an investigation can see what the device saw?
Frequently asked questions
What is a man down alarm?
An automatic alarm raised when a device detects that the worker may be incapacitated: a fall, a hard impact, a tilt (the device lying flat), or no movement for a set time. It is also called fall detection, worker down or no-motion alarm.
How does man down detection work?
An accelerometer and sometimes a gyroscope in the device or phone watch for a sudden impact followed by stillness, or for the device lying at an angle, or for no movement at all over a period you set. A pre-alarm sounds first so the worker can cancel a false trigger; if they do not, the alarm is sent.
Does a phone app do man down well?
Not reliably. A phone in a pocket, a bag or a cradle moves differently from a body, and sitting still at a desk or in a van looks like no movement. Apps that offer it trade false alarms against missed falls. Dedicated wearable devices do it better.
Does SafetyEvo have man down detection?
No. It is on the roadmap but not offered today, because we are not willing to ship a version that false alarms on a phone set down on a bench. Check-in timers and silent phone alerts cover most of the same situations; see below.
Who really needs it?
People who work alone at height, in confined spaces, with machinery, with hazardous substances, or with a medical condition that could cause collapse, where the risk is an incapacitating event with no chance to press a button. For those tasks a wearable device, and a serious look at whether the task should be done alone, is the right answer.
How this guide was written
Written by the SafetyEvo team, who build lone worker safety software and use it in their own field business. Every legal point is checked against the primary source listed below, the guide carries the date it was published and the date it was last reviewed, and it is corrected when the law or the guidance changes. It is general guidance, not legal advice for your situation.
Sources
This article is general guidance, not legal advice. For your own situation, speak to a health and safety or legal adviser.