Why don't we all have doorbells on the insides of our front doors? When confronted by a visitor with which we don't care to speak, we could discreetly press our hidden inside doorbell and trigger, elsewhere in the house, the sound of a baby crying. Or a smoke alarm. A tea kettle. Whatever.
Or hey, all four. "I'm sorry–I'd love to discuss my immortal soul, but my tea kettle appears to have set off the smoke detector and frightened my baby."
For some reason I feel like I'm ripping off the blog Ironic Sans, where my friend David posts ideas like this all the time. Go visit that, maybe.