Bouncing lasers off window panes to detect audio is a worrisome development. The counter-measure is to install dual pane windows equipped with acoustic transducers that vibrate the panes with white noise. For the device mentioned in the article, when the technology becomes available to consumers and/or is open-sourced, anyone will be able to count the occupants of any location near to them. The question again becomes one of counter-measures.
Development? The technique has been well known for a long time, I remember hearing about it in the late 90s. It isn't widely used because it isn't practical. Also, your countermeasure doesn't work if there is another reflective surface inside the room.
> Development? The technique has been well known for a long time
The difference is that these things used to be the domain of major government agencies rather than a hobbyist with a few hundred dollars and a poor sense of privacy.
The bottom line with both of these technologies is that their usecases are simply too narrow to inspire causal use.
The radar-gadget is useful if you're about to storm a house full of armed adversaries - in most other cases, you can just peek through the window or knock on the door and get much the same information.
The laser-bouncer is great for eavesdropping on people who take some effort to hide their communication - if they don't, hiding a wireless microphone or a high-capacity dictaphone is orders of magnitude simpler and cheaper.
The other countermeasure is windows angled downward so that the laser would have to be on the premises to get a direct bounce. Not viable for most homes, though.
