Here is an interesting hobby circuit of a “crank” door bell! The circuit is built around a timer 555 and a musical piezo-buzzer. The circuit works off 9 volt battery supply. One 9volt PP3/6F22 compact ...

If you’re expecting an important visitor but you just have to step out for a moment, an electronic doorbell memory can come in handy so you can see whether someone rang while you were out. Of course, ...