The subscription is quite important as it's your guarantee that their database is totally up to date. There are plenty of freebie db's but you have to question how good they are if they're free. Most are for use with SatNav systems, don't know of any that would work with a GPS camera locator.
By the way the parking sensor device above is a laser jammer not a camera detector. A variation on the garage door opener/laser jammer from Target.
If it works then it's only good for mobile speed traps, not fixed cameras, as these don't use laser. So essentially you need both GPS & laser jammer for 100% protection.