From ThresholdRPG Wiki

House Object

Doorbell is a house object which can be purchased for a player house at a cost of either 10000 coins or 18 ThreshCredits.

Doorbell can only be purchased in the front yard. The verbs available to use on the doorlbell are ring, pull, or press and the subject can be any of doorbell, bell, cord, rope, bell cord, or buzzer.

When rung, the sound will carry to every every room of your house and can only be rung once every 30 seconds. The doorbell is not a visible object and people will not know it is there unless you note its existence somewhere in your room or door description. This also allows you to call it a doorbell, a bell cord, or whatever fits with the ids listed.