How much are lazer surveillance and espionage microphones that you see in...

[Swampy_Bogtrotter]

...shows like Spooks worth? I've discovered how to make those lazer listening devices that you see on spy movies and TV shows like Spooks.
You know the sort.
A lazer beam is aimed at a window, and a sensor picks up the reflection from it. The sounds inside the room cause the glass to vibrate and the sensor picks up that vibration in the reflected lazer beam, and the device converts it to a signal that can be recorded by any regular soudn recorder.

I want to try selling these, but have no idea what they would be worth to a buyer.

[James]

I used to work for a covert surveillance team and we used to pay £800.00 - £1000.00 then for the wand and receivers.
You will need a liscense to sell it and you will need to stress to your customers the laws of eavesdropping and privacy.
One of the reasons the price is so high is to deter the average person buying it to hear what the neighbours are up to.
It is your responsibility to screen your clients and to check that they are liscensed as well.