£4 at Boots.
Just went into Tesco picked these up one for holiday and will use the other in the airing cupboard where boiler is. Wouldnt recommend use in home where kids sleep/play but better than nothing.
Installs in seconds
No batteries required
Twin-pack for 6 months protection
Spot in centre turns from brown to black when exposed to high levels of carbon monoxide and at end of working life.
Label for recording activation date
Ready for instant use, straight from the pack
Small and discreet