My wife is always leaving her phone's ringer on silent. Whenever the kids or I try to call her, she has no idea anyone is calling. With this app, I can send a text message to my wife's phone that will turn the ringer back on.
You can add any number of authorized contacts and provide each contact a password (case sensitive) that they can text to your phone to turn the ringer on.
In the Settings you can enable/disable the service.
Disclosure: Each and every text message that your phone receives will be examined by this app. No text message information is stored or relayed by this app.