often do the same, depends on access to upstairs really. much easier if they have carpet and proper floorboards, not laminate or weyrock
if its a bungalow even easier (unless they have boarded the loft)
cheap tat from B&Q and youre surprised its gone flat within 6 month? im surprised it has lasted 6 month.
some wireless alarms can have wired bellbox & detectors but you can expect to pay a bit more than £100..
Visonic's are fairly easy to install, I have fitted many of them myself in the past, but i now use texecom ricochet for all new installs. not a massive price difference and imo a far better system
if its a DIY install then a visonic may be the better choice for ease of installation
Ive not had any issues with them and cats, although some cats (more so those who have the odd 5 minutes of crazy running around) do trigger them occasionally. as above, try and go for more perimeter protection with shocks, but if you do encounter the odd false alarm you could set the detectors to double knock
4 core will do for most detectors if using EOL, although i usually use 6 core
if you do use texecom, the RKP has onboard zones too, so you can wire detectors back to there, gives you 10 zones without needing an expander