Is there an alarm that tells you when your phone has been left off the hook?

[nobodysfool]

My nan keeps leaving her phone off the hook by mistake (its a cordless one that has to click into place).
We have bought her various different types and styles but she still manages to leave it off the hook which worries the hell out of us.
In the USA they have a device that does just that but i cant seem to find one for the UK.
Any ideas?

MIne does it... im not sure how i got it, it has always made a siren cound when left off the hook. Maybe phone BT?

thanks for replying..i think all phones give off a phone off the hook noise but i need and alarm device that is LOUD so she can hear it..
this kind of thing

Gawd knows. But that would be so useful!