There are cheap PIR motion sensors available for the ESP8266. The HC-SR501 is such a module. It can be configured through two potis at the back regarding sensitivity and delay after a motion detection, before the output is reset again.
The sensor has three pins: One for +5V, one for ground, and the middle pin is a 3.3v output, which can be connected to a digital input pin from the ESP. Getting notified about motion is very easy like this.
Example code to connect the sensor:
inpin=1 gpio.mode(inpin, gpio.INT) startTime = 0 function motionStart() start=tmr.time() print('Motion detected!') tmr.delay(1000000) gpio.trig(inpin, "down", motionStop) end function motionStop() duration = tmr.time() - start tmr.delay(1000000) gpio.trig(inpin, "up", motionStart) end gpio.trig(inpin, "up", motionStart)