WASHINGTON — For better or for worse, it's rapidly getting easier for others to know where you are, sometimes 24/7.

Thanks to the explosive spread of wireless technology — particularly cell phones, car navigation systems and the Global-Positioning System — parents, employers, detectives and government agents can track your movements, with or without your being aware of it.

Many people don't realize that a cell phone, Blackberry or wireless laptop computer is constantly broadcasting its location whenever its power is on, whether or not a call is in progress.

This has led to "a new, unique ability to automatically identify somebody's location," Jed Rice, vice president of Skyhook Wireless Inc., a three-year-old location-system provider based in Boston, told congressional aides this month. "This obviously raises privacy issues."

"The type of location tracking possible in the 21st century is quite different from anything previously available to government agents," the Washington-based Center for Democracy and Technology warned in a February report.

More than 214 million Americans — 2 out of 3 — are wireless subscribers, according to the Cellular Telecommunications and Internet Association, the wireless trade organization.

In addition, more than a million cars and trucks are equipped with on-board location devices, such as the OnStar system that's available on many General Motors and some Acura and Isuzu vehicles. OnStar provides drivers with navigation maps, handles phone calls and sends signals if vehicles are involved in emergencies.

Several state transportation departments are beginning to monitor wireless devices in moving cars in order to detect traffic slowdowns and issue advisories to drivers.

"There are 40 million Wi-Fi access points — 500,000 in downtown Chicago alone," Rice said. "We know where they are, (but) we have no record of who you are. The information is anonymous."

A growing number of companies sell tracking services.

WaveMarket launched a "Family Locator" service in April that lets a parent pinpoint the whereabouts of a child using Sprint or Nextel cell phones.

Sprint sells a "Mobile Locator" service that it says can "monitor employee location in real-time, either singly or within a group, on a zoomable online map."

Trucking companies use GPS technology to track the movements of their drivers. The boss knows when a driver takes a break, violates the speed limit or departs from his unauthorized route.

John Morris, a privacy expert at the Center for Democracy and Technology, told about a rental van company that tracked a driver going 80 miles per hour. "They charged him three $150 fines," Morris said.