Buy.com has the DuPont PS-131 Self-Charging Smoke Alarm for $5.99 with Free shipping for a limited time.

The DuPont Smoke Alarm PS-131 is one of a new generation of domestic life safety products from DuPont, which combines the latest technology and innovative design to provide an aesthetically pleasing and effective contribution to your fire safety. Your DuPontTM Smoke Alarm contains an exclusive 10-year self-charging power pack. This power pack automatically re-charges from the household current when the light is on and powers the alarm when the light is off. Your DuPont Smoke Alarm requires the light to be on for a total of approximately 2 hours per week to remain fully charged, and will operate for 30 days from a full power pack without charging. The alarm will chirp approximately every minute should the power pack charge run low. Your DuPont Smoke Alarm PS-131 uses an ionization type sensor to detect the presence of smoke. Ionizationtype smoke alarms are generally more effective at detecting fast, flaming fires, which consume combustible materials rapidly and spread fire quickly.