Or they may install equipment so faulty that your system doesn't work at all.
Bottom line: Whether it's a phone call or in-person solicitation, don't give in to the pressure.
How to protect yourself
Don't let anyone into your house on a first call. Instead, ask for printed literature and a business card — a badge or ID can be forged — and use the information to check out the company. Make sure to look for information about it on the websites of the Better Business Bureau and your state's attorney general. If you decide to pursue the service, call the company to come back for a second visit.
Ignore claims that an offer is for a limited time only and that technicians are ready to immediately install the system. Reputable companies let you compare bids and engage in a comprehensive review of your security needs.
Call your insurer. You may be entitled to homeowner insurance discounts for using certain alarm companies.
Ask for all procedures in writing. If the alarm sounds, does the company first notify you or the police? Does the company have a local security patrol car? Will you be charged for false alarms? What's the early termination fee?
Expect to pay roughly $1 to $2 per square foot of your home for a complete system. Quality systems combine audible and silent alarms triggered by sensors placed throughout the home — not just on doors and windows. Higher-tech sensors can distinguish between a human and pet; cheaper ones cannot.
Sid Kirchheimer is the author of Scam-Proof Your Life, published by AARP Books/Sterling.