These motion sensor alarms seem great value at £7.99, these will be instore at Lidl from Thursday 24/10/13.
Product Information :-
110° detection angle and range of up to 8m
With 105 dB acoustic and visual alarm and 2 x infrared remote controls
Batteries and wall mounting materials included
Size approx. (cm): H12 x W8.5 x D4.5
3 year manufacturer's warranty