Dave Plowman (News) laid this down on his screen :
Just got mine installed and working. The final straw was a couple of
'auto' calls very early in the morning. Bit fiddly to set up, and was
rather p***ed off to have to pay BT almost 20 quid a year for caller ID.
Plus the 20 quid a year for the TruCall online facility.

All I now need to find out is if it triggers quickly enough to stop the
phone in the bedroom ringing.

I don't understand any of that...

As said, mine is built into our set of new BT phones. Our Caller ID is
free and I am not aware of any need to update the TruCall system. It
took minutes to set up, I just set it to filter all calls from unknown
numbers, numbers not it its list. Those unknown callers then get the
opportunity to get through by recording their name and pressing hash.

If they do that, my phones ring and I get the choice of speaking to
them, ignoring them, or passing them to voicemail.

Calls with no caller ID, don't even get the chance to state their name
and press hash - a recorded message just tells them we don't accept
such calls.

The phone never rings, unless a known number rings, or the caller gets
through the filter procedure. If I were to plug a normal phone into an
extension socket, that would ring. I do have a none wireless phone on
an extension there for emergencies and power cuts, but its ringer is
turned off.

The majority of our nuisance calls fell into the spoofed caller ID
type. Spoofed 020, 0020, spoofed local numbers, some none existent,
some 'borrowed' genuine numbers. Then lots of calls with no Caller ID.
Mostly now they use a recorded message. None have got through, but a
few genuine callers have succeeded in getting past the 'state your
name, then press hash'..

Peace at last ;o)