I was trying to get a piece of kit approved by Post Office Telephones at Dollis Hill at about the time the Trimphone came out; they had a few spares. "Do you want one, Jim?"
Took it, liked it, but Mrs Jim hated it. She kept running in from the garden to answer its distinctive warble, but never got there in time...
Turned out we had a resident blackbird who had learned to echo the blasted thing. We speculated that he might have been trying to get her out of his garden. Nah. Really?