SpeechPOD Dual contains two PIR motion sensors which detect persons at a distance of up to 6 metres. When SpeechPOD detects a person moving Left to Right across the product it will play any selected message from the SD card memory. When SpeechPOD detects a person moving Right to Left across the product it will play a different selected message from the SD card memory, therefore providing a bi-directional messaging system.