Home automation with high usefulness and low annoyance tends to rely on reliable person sensing, and [francescopace]’s ESPectre shows one way to do that cheaply and easily by leveraging hardware that’s already present on a common dev board.
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**ESPectre is an ESP32-based open source motion detector that detects movement without any cameras or microphones. It works similarly to millimeter-wave (mmWave) radar motion detectors in the sense that when a person moves, wireless signals are altered slightly as a result. ESPectre can detect this disturbance by watching and analyzing the Wi-Fi channel state information (CSI) and doing some very smart math and filtering. It’s cheap, easy to deploy and use, and even integrates with Home Assistant.
Combining a sensor like this with something else like a passive infrared (PIR) motion sensor is one way to get really robust results. But keep in mind that PIR only senses what it can see, whereas ESPectre works on WiFi, which can penetrate walls.
Since ESPectre supports low-cost ESP32 variants and is so simple to get up and running, it might be worth your time to give it a trial run. There’s even a browser-based ghost-dodging game [francescopace] put online that uses an ESPectre board plugged in over USB, which seems like a fun way to get a feel for what it can do.
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Using WiFi signal disturbances to track people might not be super accurate, but damn that’s a cool trick. Although, also a good proof of concept for how bad actors could use nothing but control over a WiFi-capable device to spy on you, which is a bit concerning…
Anyway, before learning about this, I ended up using an ESPHome BLE beacon component along with the Home Assistant app. You can configure the transmission strength in the app, so by setting it to “low” or “very low”, the ESP32 only picks it up when my phone is in the same room. It has worked a lot more reliably than some other stuff I tried.