Radar presence sensors: cover the rooms a camera can't

Why a still room is not an empty room

Unlike a passive infrared motion sensor, radar can register a person who is present but sitting still. An empty kitchen and a kitchen with someone sitting quietly in it are not confused, which is the difference between a device that reports movement and one that reports a person.

Vendors in this class make that contrast themselves. Aqara's page for the FP2 sets a PIR sensor that "Cannot detect presence when you are sleeping or sitting" against a radar sensor that "Detects presence even if you are not moving" (Aqara FP2 product page, checked 2026-09-07). That is the vendor's own comparison, not an independent test, but it is the right question to put to any product here.

The useful output is a pattern rather than an event. Was there movement in the bedroom overnight? Has the kitchen been empty since yesterday evening? Has the bathroom gone quiet for far longer than usual?

What it reports, and what it never will

Nothing to wear, nothing to charge, nothing to press

This is the practical difference between a room sensor and a pendant, and it is worth stating plainly because it is the one thing this class does better than every alternative: it asks nothing of the person being monitored. A fixed sensor is mains-powered and stays where it was installed. There is no button to reach, no strap to put on in the morning, no charging cradle to remember.

That matters because the alternative depends on the person using it in the moment. A Cambridge study followed 110 people aged 90 and over for a year and found call alarms were nearly universal among those who fell alone — and mostly unused: "In 80% (113/141) of these falls, however, the person who fell alone did not use their call alarm to summon help", rising to "97% of these 'long lies' (37/38)". The authors concluded that "Call alarms were widely available but were not used in most cases of falls that led to lying on the floor for a long time" (Fleming & Brayne, BMJ, 2008).

Read that for what it is. It is evidence about pendants, in one cohort of the very old, and it is not evidence that a presence sensor produces a better outcome — no trial shows that, and the Canadian randomized trial above found no significant effect. What it does establish is that a device requiring an action is a device that may not get the action.

The cost of asking nothing is that each room needs its own unit and its own outlet. Coverage is per room, so the price and the installation scale with how many rooms you want covered, and a room with no sensor is a room with no information.

The rooms it is actually for

In a home, this class suits the rooms where a camera would be refused and a pendant is not worn: bedroom, bathroom, hallway. It fits families at a distance who want a daily rhythm rather than a 3 a.m. buzzer — a group that is not small, since solo dwellers "represented 42% of all people aged 85 and older in private households" in the 2021 Census (Statistics Canada, The Daily, 13 July 2022). In a care home or supportive housing, it gives night staff a room-by-room picture without entering rooms or filming residents.

One unit covers one room, and its reporting stops at that room's walls. That is the whole shape of the thing:

It sits alongside a pendant and a bed alarm; it is not a replacement for either, and not for a care plan.

How it compares with the other camera-free options

Wi-Fi sensing covers the whole home from the router and cannot reliably say which room. Acoustic monitoring hears a room but needs a microphone in it, and hears nothing when nothing makes a noise. Radar fall detection sensors use similar hardware but make a claim this class does not make at all. Sensor by sensor and room by room, that comparison is set out in PIR vs mmWave vs Wi-Fi vs acoustic, and every listing's attributes sit in one table in the directory comparison.

What to ask before buying

• Does it report presence, or only motion? Ask what happens when a person sits still.
• Which ISED certification does the product hold, and is it sold and supported in Canada?
• How much of a room does one unit cover, and how many units does the home need?
• What leaves the home, where is it stored, and in which country?
• Does the vendor claim fall detection? If so, ask for the exact wording and for any real-world accuracy data.
• Who receives the alert at 3 a.m., and what are they expected to do?
• Can it be turned off, and can a resident or their substitute decision-maker consent to it?