Hi Adam
10-15 years
Not much electricity, much less than your fridge
Not sure what you mean by getting it removed people pay hundreds of £'s to have security in their house why would you want to remove it?
ADE
The detection and ancillaries would be compatible with many hard wired alarm systems available on the market today
The keypad is saying that everything is fine, the noise you can hear from the main box is the transformer.
I would advise that you get the system serviced, the person servicing it should be able to default the codes and show you how to reprogram a new one, depending on the last time it was serviced it may need a new battery, the fact that it is showing day and power is good, the transformer noise could be that the battery is drawing too much current, or it may just be a noisy transformer, hard to tell remotely. Alternately you could just ask someone to quote to update the system.