As USA Today writes:

"If the power goes out, you don't have to be in the dark. The Mr. Beams ReadyBright™ Power Outage Lighting System system features battery-operated emergency lights that automatically turn on during a power outage. Set up is simple: Plug a power detector into
a wall outlet. When the power goes out, the power detector will turn on the emergency LED lights via a wireless signal. Priced at $100, the 
ReadyBright™ Power Outage Lighting System from Wireless Environment contains a power outage detector, two ceiling lights and a stair and path light."

 

Read the full review here: http://www.usatoday.com/tech/products/story/2011-09-17/new-tech-products/50435020/1