Solution

The doorbell operates with a step‑down transformer. The primary winding is left permanently connected to the mains, and the push button is placed on the secondary side for two main reasons:

· Safety: When pressed, only the low voltage of the secondary (6–12 V) is handled, with no risk of electric shock to the user.
· Circuit protection: Repeatedly connecting and disconnecting the primary would cause current spikes and electric arcs at the switch. In contrast, the transformer at no‑load consumes very little (only the magnetization current) and suffers no wear. This way, the doorbell is always ready and the system is more durable.