Modernise Alarm System

Having recently moved into a new property and having the circa 1995 hard wired alarm system serviced, it appears not only do the panels look archaic but the two outdoor bells aren't functioning. So it appears it's time for a complete overhaul. (Current system Scantronic 9800)

Am I limited to an upgrade from the company who installed the system or can I get quote from various suppliers?

Do I really need two outdoor sounders on a quiet country lane with zero background noise?

It was suggested I replace all my indoor sensors, is this really necessary as they all seem to react fine as I walk past!

A system of that age most installers would recommend a system upgrade.
Get a few quotes so you can compare price and equipment specification.
Professional installers will do a risk assessment of the property and provide a quotation based on that assessment.

By system upgrade you mean replace everything? I assume the existing wiring in the walls will be ok for any new system?

What does anyone think about whether two sounders are needed or if one would suffice. Strangely neither of the two existing sounders are visible from the front of the property as a visual deterrent!

It really depends on how the system is setup.

for example, we would advised rewiring if there were loads of devices on one circuit.
If the system is powered up and functional then it can be easily tested, you already suggest the bells are not working but not established why, ie cable damage, blown fuse, bell died.

Without seeing the property or area its difficult to say as to what is the best options, can your nearest neighbours see or hear the bells for example?