Old phone that just had an alarm sound, huh?

[#1]

https://www.amazon.co.uk/BT-Response-plus-Telephone-Answerphone/dp/B000060OEW I have 15 year old one of these and just now the phone had an alarm going off like a old school police siren. Picked up the handset and it stopped, no idea what it was for. It doesn't have its power pack plugged in for the answer phone as I just use 1571 for that, first time I have every heard it in 15 years and no idea why this alarm just went off, any ideas?

[#2]

Sounds like the alarm you get when the phone has been left "off the hook"

[#3]

The handset was definitely in place, maybe the switch it sits on is starting to fail, so guess a new one is due

[#4]

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@PeterLoftus wrote:
Sounds like the alarm you get when the phone has been left "off the hook"

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Almost certainly that's what it was. Known in the trade as the howler.