Installing a security system has long been considered the domain of professionals — uniformed men and women who build an electronic shield around your home and monitor it from a command center.

At least that is what the commercials always seem to suggest.

But a new breed of home-security systems promises to be simple enough to install without any professional help, cutting the cost of traditional alarm systems by taking advantage of technologies like wireless connectivity and battery-operated sensors.

Some of these systems even allow you to monitor your home yourself, using a Web browser on a computer or a smartphone. Following is a roundup of new ways to keep your castle well guarded.

The First Line of Defense

Companies like ADT and Brinks offer a full alarm installation at a subsidized price, but they more than make up for the discount with their monthly monitoring fees. These systems usually involve whole-home wiring and, although they offer perks like video surveillance and 24/7 monitoring, most of these features can be easily replicated with do-it-yourself kits.

The best thing about the new D.I.Y. services is that they are wireless. While many people actually enjoy drilling holes in doorjambs and walls, most would prefer to stick a few wireless, battery-powered sensors to the windows and call it a day.

There are simple security tools you can add to almost any home without much fuss, and some of them cost as little as $10. General Electric sells a number of inexpensive products under the GE Smart Home name, including an Automatic Security Light Kit ($25) and an easy-to-install Window or Door Alarm ($12) that attaches to your door and doorjamb, and squeals loudly when the door is opened. This is best for rarely used storerooms or closets, as well as gates and windows you would prefer to keep closed for safety’s or security’s sake. GE also sells a $10 doorstop alarm that activates when someone tries to open a door. Because it is positioned on the floor like a doorstop and requires no installation, travelers can use it to alarm hotel-room doors.

Higher-Security Measures

For those willing to do some work, there are full security systems that take a little effort to install but cost far less in the long run than professional systems, thanks to less-expensive monitoring fees. These kits usually have multiple sensors, including small attachments that monitor windows and doors, as well as motion detectors. Most require few or no tools — a bit of double-sided tape holds most sensors in place — and some are designed for apartment dwellers who don’t want to damage the paint on doors or windows.

All of these systems are almost completely wireless. Except for the base stations, which connect to a landline, the sensors, buttons and keypads rely on Wi-Fi or other wireless technologies to cast a wide net around your house or apartment.

LaserShield (lasershield.net) sells a kit that costs about $700 and includes a base station, three wireless window and door sensors, a motion detector, two key-fob controllers and a smoke detector. It connects to the company’s monitoring service through your telephone line, although a cellular connectivity solution is also available. Monitoring is about $30 a month, and add-ons include wireless cameras and a “flood detector” to alert you to water in low-lying areas like basements.

LifeShield (lifeshield.com), provides approximately the same package for about $300, including eight sensors, a smoke-alarm siren detector, a base station and keychain remote. The self-monitoring plan allows you to receive alarms by text message or e-mail, and you can control the security system from any computer connected to the Internet.

For true D.I.Y. security on a budget there is the Q-See Wireless security system, available at sites like Newegg.com for about $60. The kit includes five door sensors, one motion detector and two keychain remotes. Instead of alerting anyone, the Q-See simply sets off a high-pitched alarm, which may be enough to dissuade casual thieves.

Finally, there’s SimpliSafe (simplisafe.com), a new monitored system that starts at $200 for a portable apartment-dweller’s kit or $300 for a more complete kit with four door sensors, a large panic button and two motion sensors. When you move, you simply remove the sensors and reattach them using double-sided tape. SimpliSafe’s monitoring service is $15 a month and requires no phone line; the system uses a cellular wireless connection to stay in touch with the SimpliSafe monitoring service.

For those looking for video security, each of these kits has a video option. Major manufacturers of Web cams, like Logitech, are also getting into home security with products that will keep an eye on your premises remotely. A new set of Logitech cameras, available in August, will allow you to place cameras indoors and out, and receive e-mail and text messages when something moves in the field of vision.

And a company called Vitamin D (vitamindinc.com) has free software that turns any Web cam and some wireless video cameras into a security camera, allowing your stay-at-home computer to act as a home security system, sending e-mail messages when the software detects unusual activity. (NYT)