There's no arguing the desirability of a professionally installed, whole-home security system with around-the-clock monitoring. There's only one problem: You're probably not eager to pay the monthly service fee, let alone the upfront cost. A lot less expensive are solutions like the GE Personal Security System, a set of window and door sensors that, if triggered, emit an ear-piercing, 120-decibel alarm. No, the system isn't fancy, but to deter a would-be burglar, you may not need anything more than a burst of very loud noise at precisely the right time. Available at Amazon; $20.