So instead of plugging in a lamp, you plug in something that makes noise and the outlet gets turned on. You could plug in a radio, a vacuum cleaner, whatever you want.
It’s $55.
Here is the website link. It says:
“Alerts to any important sound: phone, kitchen timer, baby, etc.”
http://www.harriscomm.com/sonic-alert-traditional-system-uss-360-universal-sound-transmitter.html
And the manual: