Disclosed herein are a monitoring device and systems utilising one or more such monitoring devices. The monitoring device comprises a protective housing containing: a passive infrared (PIR) sensor; a power supply a microcontroller; and a wireless transceiver. The power supply powers each of said PIR sensor, said microcontroller, and said wireless transceiver. The microcontroller is adapted to send an alert message, via said wireless transceiver, upon receiving a motion detection signal from said PIR sensor.