I found a great deal on a First Alert CO400 Battery Powered Carbon Monoxide Alarm, on sale for 40% off.
It is on sale for $27 and usually sells for $45.
These are necessary in any house.
- Battery-operated carbon monoxide alarm
- Uses electrochemical carbon monoxide sensor–the most accurate technology available
- Simple to use silence/test button, low battery warning, end-of-life timer
- 1-9V Battery or 2-AA Battery (included) power source.
- 5 year limited warranty
Here is a link to the sale.