Do GPS jammers really work?

Yes GPS signal blocker work ,One demo I saw way back was a jammer the size of a cigarette lighter that was powerful enough to jam the GPS planes would use for an instrument approach. GPS is tuned to very faint signals from satellites and it’s easy to overpower them.If the jammer has any strength at all it’s going to light up on the ADF-Automatic Direction Finders of several agencies, public and covert, and they’ll pinpoint it in a second by triangulating, and find bug.