Pyroelectric motion sensor HC-SR501. At a price of less than one dollar, the sensor has a number of positive qualities, namely: power supply from 5 to 20 volts, motion detection zone from 3 to 7 meters, turn-off delay from 5 (in practice, although the estimated time using the Tx formula is at least 2.5 seconds) up to 300 seconds. Standby current <= 50 microamps;
Operating current consumption <= 110 microamps. Viewing angle from 120 to 140 degrees.
Cost: ~ 58