Yantan, do you have a doorbell? If not, get one like ours, the bellpush just sticks onto the front door frame then the receiver plugs in and there is also a freestanding one that you can put anywhere in the house, or if you're hoovering, in your pocket. They are pretty loud, I hear it above the radio or the noise of the hoover. Reminds me, I must change the ring on mine, it's got Santa Claus is coming to town at the moment!