Also, don't forget that you can TOTALLY guarantee that you won't exceed the relay's current limits by using a transistor in open collector mode.

When we wire up relays, we go directly from a power supply through a set of metal contacts. A mistake can end up in things being fried, really bad if the fried thing is inside the "doorbell." If we use a transistor instead, we can easily make a circuit that will keep anything from blowing up if there's a short circuit, while having it work properly. Unfortunately this approach is one step into "science project" territory, but it can be really helpful.