It's a device that produces a sound of a woman screaming. People buy them as a joke on the public or used as a way of breaking up a person's partner.
It is meant to sound like a woman getting attacked or raped.
What's loud and shrill and ruins your orgasm?
A rape alarm.
John: Look at this rape alarm that I just bought.
Dave: What does it do?
=John activates the device and screaming can be heard in the house=
Dave: What the hell?? Why would you get something like that?
John: I'm going to try to use it to get my brother's girlfriend to dump him.
The act of waking a sleeping woman by having sex with her.
Reginald: "My girlfriend was snoring like a pig again last night, so I decided to give her the old rape alarm."
Winston: "How did that work out for you?"
Reginald: "Well it stopped the snoring... but then there was a great deal of shouting and screaming."