Ultrasonic sensor
Budget: $15 – $30 USD
I have two ultrasonic sensors (Sensor A and sensor B) connected to two Esp8266 and a raspberry pi where is installed a server Mqtt. When a person passes at a distance less than 80 cm from sensor A starts a video on the raspberry. If a person passes first in front of sensor B and then in front of sensor A the video must not start (in practice sensor A must remain inactive for x seconds. After x seconds it will be active again).