Td5 alarm went off

My alarm went off the other night for no reason, the indicators flashed and horn ommitted a continuous tone for about 10secs. The BBUS didn't sound at all.
Should the alarm be a beep beep beep rather than a bèeeeeeeeeeeeppppppp ? Sure it was when I tested it once before?
Also can I check the BBUS of the car as that also used to work.
Many thanks.

Easiest way to test the BBUS is to disconnect the battery without first doing the battery disconnect procedure which disables the BBUS. If it's working, it will sound. But the horns and flashers won't because the battery is disconnected.

Wimblowdriver said:

Easiest way to test the BBUS is to disconnect the battery without first doing the battery disconnect procedure which disables the BBUS. If it's working, it will sound. But the horns and flashers won't because the battery is disconnected.

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It doesn't work from the internal battery as I presume it's dead many years ago but shouldn't it work of the 12v feed from the vehicles battery regardless of the state of the internal battery? (When the alarm goes off)