Update: Deal over.

Kidde Battery-Operated Ionization Sensor Compact Smoke Detector Alarm – Link

Amazon has this currently marked down to only $4.44!

• Battery operated Ionization sensor compact smoke alarm
• 9 volt battery, mounting hardware and installation guide
• Four inch diameter discreet design
• Test button tests unit’s electronic circuitry horn and battery function
• UL listed and is backed by a 3 year limited warranty
• Easy installation
• Battery operated 9V battery included