Groupon offers the Activator RX-9 Infrasonic Home-Security Alarm for $19.99 with free shipping.

What makes this deal hot:
You save a total of $79.96 off of the retail list price. That's the lowest price we could find currently.

What this does & Why you need it:
This security alarm features monitors the whole house, emitting a loud siren when it detects doors opening, windows shattering, and more.