Burglar alarms are not the be-all and end-all of home security. There are plenty of other things you can install in your home that will help to stop a burglar from gaining entry, and many of them are very simple and inexpensive.
The key is to secure the possible points of entry. This means that doors should be made of strong, solid material (definitely not glass or plastic), be properly secured to their hinges and have tamper-resistant locks. For ideally, you should have an extra deadbolt that you put on at night, made from very strong metal.
Very important for windows part, it should be made from toughened glass, preferably double-glazed, so that they are almost impossibly easy to break. Although window locks are relatively uncommon, they help greatly with security, and you should consider installing them. If your house has windows in a position where they can be easily and discreetly accessed from the street, such as basement windows, you should consider putting metal bars on them.
It’s also important for your garden to be secure, as far more burglars enter through the back of your house than the front. This means that your fences should be high and have some kind of anti-climbing measures (spikes or anti-climb paint can work well). If you do not like fences, get big hedges instead.
Another thing to consider is getting a dog, surprisingly effective against burglars, who don’t generally want to mess with dogs if they can avoid it. For this strategy to be more effective, put up a ‘beware of the dog’ sign. Smaller dogs are not so great for this because they are not generally scary, something like a big German Shepherd works best, not only because of their size but because of the strong guard instincts that cause them to be hostile to strangers.