The ZH-28 guard was a model of security droids manufactured by the Stonewall Labs company during the Imperial Period. This droid had a humanoid shape and was as tall as a medium-sized Human. The ZH-28 guard was able to fight using ranged weapons.
ZH-28 guards were manufactured by Stonewall Labs prior to the Battle of Yavin. When the Stonewall Labs facility on Naboo was closed, security droids remained activated. Several ZH-28 guards, SWL-5 overseers, LC-92 antagonists, Mechthorians and B1 battle droids continued their patrol programs in the laboratory and in the surrounding area. Circa 1 ABY, a spacer was trying to acquire an experimental Old Republic droid module from a droideka in the Stonewall Labs facility. The spacer entered the laboratory and fought several ZH-28 guards to finally access the module.