Hi, will alarm cable run outside to garage that is exposed to the elements suffer any detrimental effects due to heat/cold and cause nuisance tripping? Also I have fitted a couple of alarms and run cables close to mains cable in places without any probs, just how vulnerable are cheap domestic alarms to mains inteference?
Thanks.

As Lectrician says, over time the cable will deteriorate but your yearly service will show up any deterioration so I shouldn't have thought you should see any sudden unexpected faults.

I would avoid running mains and alarm\data\telecom cabling as the induced voltage from the mains cable can cause damage and\or nuisance activations. There is also the fact that it's considered as 'rough' and the fact you are DIY'ing the job isn't an excuse for not doing it properly.

Cheap domestic alarms as available from B&Q and the like are susceptible to inteference and false alarms when they are fitted correctly, theyre generally crap from day one to be fair. They will be more susceptible than a professional, branded alarm as they [B&Q alarms] will use cheaper components with lower tolerances to spikes\inteference.

When I said a professional alarm I meant professionally supplied, installed, serviced & maintained.

If you're going to be fitting it yourself you may as well carry on with the B&Q one, a professional system will not be of any benefit to you.