Microphone Blockers
How to choose a microphone blocker
How they work
These emit ultrasonic sound above the range of human hearing. Microphones pick it up and it overwhelms their input, so audio recorded in the room comes back unintelligible. People in the room carry on talking normally. The approach is preventive rather than investigative: rather than sweeping a room before every meeting and hoping you found everything, you make recording ineffective regardless of what is present or where it is hidden.
Choosing one
Coverage area decides which model suits the room: the room unit here covers 360 degrees out to eight metres, which is a whole boardroom, while the portable units cover about six metres in a 270 degree arc, enough for a meeting table. Several are built into ordinary objects, a speaker, a power bank, an air purifier, a car air freshener, so they sit on a table or in a cup holder like the objects they resemble. Portable units suit meetings in changing locations; the car unit runs from a USB port.
Compare the types
 Room unit |  Travel unit |  Speaker style |  Car unit | |
|---|---|---|---|---|
| Covers | 360 degrees, 8 metres | 270 degrees, 6 metres | 270 degrees, 6 metres | 360 degrees in a cabin |
| Looks like | A desktop unit with a remote | A desktop air purifier | A Bluetooth speaker | An air freshener in a cup holder |
| Runs on | Mains, or about three hours on battery | About three hours on battery | Battery, voice activated if you want | USB C |
| Suits | A boardroom | Client offices and hotel suites | A meeting table | A conversation in the car |
| See | Room Voice Recorder Blocker | Travel Voice Recorder Blocker | Speaker Voice Recorder Blocker | Car Voice Recorder Blocker |
Buying guides
Counter-Surveillance Buying Guide NZHow to find hidden cameras, bugs and trackers
Voice recorder blockersJump to this section of the Counter-Surveillance Buying Guide
Related
Counter Surveillance Listening Device Detectors Hidden Camera Detectors
Common questions
Can people in the room hear it?
No. The output is above the audible range for adults, though some people report a faint sensation of pressure.
Does it affect phone calls?
A live call in the room will be affected the same way a recording would.
Does it stop cameras?
No. It affects microphones only. To find a camera, see hidden camera detectors.
Are voice recorder blockers legal in New Zealand? NZ law
Yes. These are acoustic devices: they emit ultrasound that overloads microphones nearby and they transmit no radio signal. Radio jammers, which block phone, WiFi or GPS signals, are prohibited in New Zealand under the Radiocommunications Act 1989 and cannot be imported, sold or used. Nothing on this page is a radio jammer.