Detect whether a room is occupied without cameras by installing a cheap ESP32 sensor that reads changes in Wi-Fi signals.
Turn lights on automatically when someone enters a room using a Home Assistant automation triggered by the ESPectre binary sensor.
Alert yourself when a space that should be empty, like a server room, shows unexpected movement activity.
Requires an ESP32 microcontroller (around 10 euros) and a running Home Assistant instance with ESPHome installed.
ESPectre is a motion detection system that works using Wi-Fi signals instead of cameras or microphones. When a person moves through a room, their body disturbs the radio waves traveling between a Wi-Fi router and a small sensor device. The sensor, an ESP32 microcontroller costing around 10 euros, picks up those disturbances and uses them to determine whether the room is occupied or empty. The technical name for what the sensor reads is Channel State Information, or CSI. The project processes this raw signal data through a series of steps: stabilizing the hardware gain, automatically selecting the most useful frequency channels, filtering out noise and statistical outliers, and then classifying the result as motion or idle. A newer machine learning mode, added in version 2.5, runs a neural network directly on the device and skips the manual calibration step. The system integrates directly with Home Assistant, the popular open-source home automation platform, via a component called ESPHome. Once set up, each sensor appears in Home Assistant automatically as a binary sensor showing motion or no motion, along with a numeric movement score and an adjustable detection threshold. You can use these in any Home Assistant automation, such as turning lights on when someone enters a room or sending an alert when a space that should be empty shows activity. Setup requires no programming. Configuration is done in YAML, which is a plain-text format that looks like a structured list. The README estimates 10 to 15 minutes for the initial setup. Multiple sensors can cover multiple rooms, each reporting independently to the same Home Assistant instance. On placement, the README recommends positioning the sensor 3 to 8 meters from the router and at desk height, roughly 1 to 1.5 meters off the floor. Metal objects between the router and sensor reduce accuracy. The system works through ordinary walls because Wi-Fi signals pass through them, and it requires no physical contact or wearable device from the people being monitored.
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