I am curious if Gatekeeper droids are capable of walking in Star Wars or if they are permanently in the doors you usually see them in.
According to Star Wars: Droidography it would seem that no, they cannot walk or move around as they are simply just the stalk and eye.
The TT-8L Gatekeeper is a surveillance droid commonly used to screen visitors at ultraexclusive locations. Although it isn't much more than a simple photoreceptor mounted on a retractable eyestalk, this droid is adept at keeping out the riffraff so the rich and superrich can enjoy their luxurious lifestyles in peace. One of the droids was installed in an elevator on the Wheel, and even though we became good friends, she still wouldn't let me into the Upper Ring.
According to the New Essential Guide to Droids, the standard TT-8L ('Tattletale') droid is affixed to the floor by a brass mount. Other models (like the TT-8L/Y7 that Jabba uses) are installed directly into a door or entrance-way. In either case, the droid is immobile.
The TT-8L is little more than an eye on a stalk. It remains in a fixed position for its operational life, usually installed near a doorway or inside a lobby. An approaching visitor’s footfalls trigger the unit's audio sensors, whereupon it scans the newcomer, compares physical parameters against its internal database, and announces the guest's arrival to its master, who can either admit the visitor or request further observation.
Equipped with a snake-like body stalk cast from antique brass, the TT-8L XSS is bolted to the floor but allowed a limited range of movement through its multiple joints. Its blue-tinted-glass optical lens functions much like a pair of macro binoculars and is protected by a bronze shutter when inactive.
The TT-8L/Y7 is designed for direct installation in a door, a door frame, or an entranceway alcove. Its rigid body stem lacks the serpentine fluidity of the XSS frame, possessing only a single socket joint at the base of the trunk. All unnecessary ornamentation has been omitted in favor of a basic black shell of resilient durasteel