In 40 seconds
A professionally installed intruder alarm in the UK usually costs roughly £400–£1,500, with most homes landing around £600–£900 for a complete wireless system. A bells-only alarm just sounds a siren on site and has no ongoing fee; a monitored alarm adds a 24/7 Alarm Receiving Centre and a subscription of roughly £15–£45 per month. Wired and wireless systems work out broadly similar once installed, with wireless cheaper to fit and wired free of signal issues. An alarm can lower your home insurance premium, often by around 5–10%, but many insurers only count it if it is fitted by an NSI or SSAIB-approved installer — and police response needs a URN, which in turn needs a monitored, professionally certified system. The honest answer is always a range, because it depends on your property and the grade of system.
Most alarm guidance is published by the companies selling and monitoring the systems, so the numbers tend to be optimistic and the contract terms glossed over. The pages below give honest cost ranges, explain bells-only versus monitored and wired versus wireless fairly, set out what a monitoring subscription actually buys, and explain the insurance and police-response rules — before you take a single quote.