Yeah, seeing how better and cheaper cameras are sold every day I thought that it might be plausible.. and then it apparently isn't.. yet. Maybe with a cheap telescope :)

A covert camera placed near the keyhole is probably a better solution anyway, because most people don't flash their keys when just walking on the street (maybe when unlocking a car, but with keyless that's becoming rare).

Used lenses from 30 years ago plus a DSLR from 15 years ago plus a suitable adapter will do the job, and may be in the price range with a bit of bargain hunting.