The primary doorbell (located on the second floor) isn't audible from the third floor, so we installed a magnetically coupled RF gateway to cause a secondary doorbell to ring on the third floor. A reed switch was soldered across the button for a remote doorbell transmitter unit, which was then placed near the solenoid coil of the primary doorbell. When the primary doorbell rings, the magnetic field of its solenoid trips the reed switch. This then closes the circuit on the doorbell transmitter, which sends an RF signal to the secondary doorbell receiver on the third floor.
