(Somewhat related to this unanswered question: Doorbell constantly rings even after replacing switch but not an exact duplicate)
My house had a modern wired doorbell (wired using Cat5e, if it matters). I don't know exactly how the push-button, transformer and bell are wired. The bell unit is the type that has an electromagically-driven hammer that strikes the bell twice: once when the button is depressed and again (with a different tone) when the button is released.
The exterior push-button was replaced with a Nest Hello video doorbell a few months ago – and since then, every few weeks one of the doorbell hammers vibrates and sometimes strikes the bell.
The Nest Hello doorbell system wires the push-button the same as before using two wires for power, but the the "signal" wire pair instead go (what I think is) a Nest wireless signal receiver which closes the circuit to make the bell ring – so the electrical path is much shorter, and has less resistance compared to the old button – so I'm assuming this causes voltage spikes from the transformer to cause the bell hammer to be actuated erratically.
What's the fix? I've read that it's as simple as putting an electrical resistor in the signal path, but what resistor rating do I need?
Best Answer
While I guess it's possible that fluctuations in the Nest Hello's power usage could cause the doorbell hammer to move, I wouldn't expect it to be enough to make the doorbell actually ring.
If you add a resistor, I imagine it should be only a few ohms, but it needs to be able to handle a fair amount of power (around 25 watts, from what I've read). It could also prevent the Nest Hello's battery from charging correctly.
Before you start messing around with resistors, try Nest's advice. You might need a new doorbell transformer.