Strat:

That could likely work. It would work best, I think, if you toggled the output. e.g. pushed it twice.

Bob:

Want to evaluate the smart relay some more?

Now it's like 6 or 7 inputs, 1 or 2 outputs.
3 from manual
3 from telephone
1 - called test mode (no siren - might be able to program)
1 - Light output
1 - siren output
1 - light for telephone error (input high more than 1 minute)

You really don't want the telephone circuit to interfere with the manual mode if someone forgot to press it twice.

Your warning mod should be easy to do too using the smart relay.