More sophisticated voyeurs may use spy gear that has its own hot spot for live streaming. So it’s a good idea to check for other Wi-Fi networks in the vicinity that have a strong signal. But that won’t help if the device is recording everything onto a tiny memory card for the peeper to retrieve later.

If you want to be more comprehensive in your sweep, several do-it-yourself counter-surveillance tools are available. Among the easier-to-use devices are specially designed camera lens detectors. They cost $200 to $400 and emit a circle of superbright red LED strobe lights. When you scan the room looking through the viewfinder, even the tiniest camera lens will appear to blink back at you, giving away its location.

“I used to sell mostly cameras, but in last few years it’s more detection devices,” said Jill Johnston, chief executive of KJB Security Products in Nashville. “There are just a lot more things to spy on you with. It’s really changing our business model, to be honest.”

Also popular are radio frequency, or R.F., detectors that can pick up signals emitted by surveillance devices. While you can get them for as little as $40, the better models start at $300 and can cost as much as $8,000, depending on their ability to analyze and differentiate signals.

Like old-fashioned metal detectors, R.F. detectors often produce a beep or tone that gets louder the closer you get to a transmitting radio signal. The more expensive versions have digital displays that detail the various radio frequencies detected and where they may be coming from.

Most environments today are filled with radio signals. Unless you get the most expensive gear and the associated training offered by the manufacturer, you’re going to have a hard time knowing whether your place is bugged or you’re picking up a signal from your neighbor’s Wi-Fi or your wireless computer mouse or Bluetooth speaker. To reduce the number of false positives, security experts recommend first turning off or unplugging all your devices before you start your scan.