Usually "doubles" as a garage door opener is the sales pitch! There was one in my Porsche until I removed it before selling a year or so ago. Never used it as far too iffy.
Usually if a error code is produced on a police laser it is flagged at DVLA. If it gets flagged again a visit from plod is inevitable. They find, remove and confiscate the equipment and a hefty fine ensues. There were several cases a few years ago and the current one is not unusual but seems to have got a fair bit of publicity.
The idea of the device is to give you an instant audible warning and allow you to brake and possibly reduce below the limit or at least reduce. The mistake this guy made was to have the time delay for it to switch off too long. If it switches off 1 or 2 seconds after a hit then the laser has a second go and even if above the limit you should if reactions are good enough be able to reduce your speed a fair bit. If they eventually get a reading within 4 to 8 seconds or so which seems to be the tolerance, they may well put the initial error reading down to a genuine glitch and be satisfied with the reading produced.
I think in the current case it was poorly sited when put in originally. Nowadays many cars have cameras recording a journey so a laser jammer shouldn't be that noticeable placed even in view and perhaps is more conspicuous if a poor attempt to hide it is made. Let's face it with cameras, sat navs, mobile phones and tablets all readily on view in many cars a jammer would be quite inconspicuouse even displayed upfront. Whatever, it's a risk to use one so I certainly wouldn't use or advocate one. The cost of such and the attendant risk outweighs the utility in my view.
Not an offence to own one and have it installed but switching it on is.