Airwick Freshmatic and cheap refills

I bought an Airwick Freshmatic a couple of months ago for the bathroom. It gives an automatic squirt of airfreshner every 30 minutes or so. Here in the UK, a replacement aerosol can to go in the device costs about £2.50 but there are cheaper ones for about £1 - but not made by Airwick.

The devide wants about non-genuine refills but I tried anyway. The replacement fitted OK but afte one squirt the red light on the device started flashing to show it had detected a refill it did not like. Question was - how did it know?

I took a good look and found some black/white bands on the side of the genuine refill nozzle and a small photosensor on the device to read these marks. As the nozzle went down to give a squirt, the sensor would see a change from black to white and so knew all was OK. My cheap refill did not do this - but a white stripe painted on the nozzle (I used the old typist correction fluid) was enough to fool the device and let me carry on.

Cheap refills for me now! Sorry Airwick (Reckitt-Benkiser)