Whether you want to figure out how many students have attended your lectures or how many evil aliens have held your space force brothers hostage, you can now use Wi-Fi to count them.

The system was created by researchers at the University of California, Santa Barbara, and uses a single Wi-Fi router outside the room to measure attenuation and signal drop. From the release:

The transmitter sends a wireless signal, and its received signal strength (RSSI) is measured by the receiver. The receiver only uses this type of received signal power measurement to estimate how many people are in the room-this estimate closely matches the actual number of people. It is worth noting that the researchers did not perform any prior measurements or calibrations in the area of ​​interest; their method only has a very short calibration phase and does not need to be done in the same area.

This means that you can simply walk to a wall and press a button to calculate with a high degree of accuracy how many people are walking around. The system can currently measure up to 20 people.

The system uses mathematical models to "see" the people in the room based on signal strength and attenuation. The system uses off-the-shelf components, they tested it in multiple locations and found that their total accuracy was two people or less, and there was only one Wi-Fi device nearby.

The body and objects basically absorb Wi-Fi when they move in the room, so that the system can find discrete things in the space. Unfortunately, it does not yet map their location in the room, and this feature may be more helpful in the future.