Alarm unit chirping - does this indicate low battery?

[MarkB]

We have Veritas 8 security alarm (installed 7years ago).
The outside alarm unit has started intermittently "chirping".
Not the full alarm sound, but a chirp - something like you get from some car remotes, but much louder, and repeated.
No sign of anything unusual on the unit in the house. Entering our code and/or pressing Reset button does not necessarily stop it - possibly stops after a while, sometimes to restart again.

According to some notes from the installers (Redcot of Manchester), the external unit is "Pyronix Bell, Self-actuating audible warning unit with strobe...".

Is it an indicator of low battery or something? (My understanding is that there is a battery in the alarm unit that is constantly charged from the mains)

 

[Lenp]

If the outside alarm signal is self contained, meaning it only requires a power source to activate, have you checked the 'off' voltage to the signal? We have had other panels with electronic swiching, transistors or mosfets, that are breaking down and allow a small voltage to pass when they are supposed to be off. This voltage can do strange things to the signal but often does not cause it to operate as expected. Replacing the offending part solves the problem.
Good luck,

Len