I don’t know about other countries, but I’m pretty sure using a wide band jammer in a built up area in the US or UK will get you noticed and imprisoned in a very short period of time... People will definitely notice.
They weren't wide band jammers, but cell tower spoofers were known to be in place in Washington DC since at least 2014.¹ They were widely suspected to be operated by foreign intelligence services, which was recently confirmed.²
So "people will definitely notice", but if you're Israeli intelligence you'll get away with it anyway.
It's not so easy to find them when they are intermittent and mobile. The prime example is truck drivers who want to briefly disable the GPS tracking systems their company put on their trucks. One of these guys was occasionally driving past a major airport...
If one thought the FBI (or a partner or ex-partner) was prone to putting a GPS tracker in one's car, one might grab cheap jammer from a Chinese e-commerce site for $20.
This is all for simple omni-directional jammers, whether chirp or wideband. Directional jamming of an aircraft is simple, and let's you put lots of energy on the target and also mask your transmission from surveillance systems. Sophisticated systems don't simply overwhelm the receiver, they trigger decoding errors, and with much less power.
The full scope of the problem is masked at present. It is relatively trivial to provide fake GPS signals so as to seduce a target receiver (e.g. mobile phone, plane GPS system) to believe it is somewhere else entirely, or off track by hundreds of meters. If a plane believes it is elsewhere, and transmits that via ADS-B, it could easily cause havok.
>I’m pretty sure using a wide band jammer in a built up area in the US or UK will get you noticed and imprisoned in a very short period of time
How are they going to find you if dropped the jammer in someone else's trashbin? If you time the collection schedule just right, you can get a week or two of jamming assuming your battery lasts that long.
Hah, devilish idea. I was thinking you could stick them in Lime scooters but once one was found the jig would be up.
Ideally you'd want something where people would earn money (bitcoin?) for operating it, they just stick it in their bag when they catch a bus/train somewhere, it only turns on briefly/sporadically, when commanded, etc.