Honeywell XC70-EN Battery Operated Carbon Monoxide Detector £20.95 @ Amazon

As far as I am aware - camelcamel graph says so anyway, this is the cheapest price that this product has been. I was in the market for one of these kinds of devices and thought that I would share because it is a good deal but ALSO because I feel strongly that everyone should have one of these in the home. If 100000 people got one to save one life it would be worth it.