My advice is to buy a safe in which to keep your valuables (old gold etc), it is also a good location for important documents such as passports etc. You can buy one from around £20 – similar to those found in hotel rooms.
Next consider an alarm, best buy a wireless type to make installation easy (circa £100).
Next consider a cctv security system, again they can be purchased from less then £200.
Imagine you are your local neighbourhood scum – which house are you going to burgle, the one with an alarm & cctv security system, or the one without?