A common question asked about sound activated recording spy cameras is how it works and how loud of a sound does it need before the triggers the recording mechanism.
For example, if someone was moving about in a room would it begin recording or would the sound have to be louder. On the other hand, would passing cars outside the house activate the recording.
The microphone in these devices are constantly listening for sound and when the volume reaches a predetermined dB level it starts recording. Depending on your situation sound based recording could be a great benefit. The other options would be motion based recording or thermal motion sensing recording.
Sound Activated Spy Cam
http://www.spycameras.com/item,dvrm-8ga,ultra-mini-dvr-camera.html
Mini voice recorder
http://www.spycameras.com/item,mvr-088,mini-voice-recorder-w-12-hour-battery.html
To get a better idea of what a dB level is, take a look at this chart of common decibel levels.
| Decibels (dB) | Degree | Sound Source |
| 225 | Deafening | 12″ Cannon @ 12′ in front and below |
| 195 | Deafening | Saturn rocket |
| 180 | Deafening | Aircraft at take-off |
| 160 | Deafening | Ram jet |
| 150 | Deafening | Turbo jet |
| 140 | Deafening | Artillery fire |
| 130 | Deafening | Threshold of pain, decibels at or above 130 cause
immediate ear damage. Hydraulic press, pneumatic rock drill |
| 120 | Deafening | Riveter, chipper, thunder, diesel engine room, fireworks display |
| 110 | Deafening | Punch press, close to a train, ball mill |
| 100 | Very Loud | Passing truck, home lawn mower, car horn @ 5 meters, wood saw, boiler factory |
| 90 | Very Loud | Decibels at or above 90 regularly cause ear damage. Noisy factory, truck without muffler |
| 80 | Loud | Noisy office, electric shaver, alarm clock, police whistle |
| 70 | Loud | Average radio, normal street noise |
| 60 | Moderate | Conversational speech |
| 50 | Moderate | Normal office noise, quiet stream |
| 45 | Moderate | To awaken a sleeping person |
| 40 | Faint | Average residence, normal private office |
| 30 | Faint | Recording studio, quiet conversation |
| 20 | Very Faint | Whisper, empty theater, ticking of watch |
| 10 | Very Faint | Threshold of good hearing |
| 0 | Threshold of excellent youthful hearing |
Read more: http://home.earthlink.net/~dnitzer/4HaasEaton/Decibel.html
