In article .com,
Murmansk69 wrote:

I'm looking for a device like a cordless doorbell but with an infrared
detector rather than a push-button.

Friedland wirefree door chime plus extra PIR sensor
http://www.tlc-direct.co.uk/Main_Ind...es_Index/Door_
Bell_1_Wire/index.html. Scroll to the bottom of the page for the
battery powered PIR sensor

--
Mike Clarke