G-Shock Watch GMA-P2100 GMA-P2100-4AER. Designed especially with brave adventurers and adrenaline junkies in mind, G-Shock watches are made to be entirely shock-proof along with fantastic robustness and multi functionality including chronograph function, water resistance and more. The G-Shock watch brand was first founded by engineer Kikuo Ibe in 1983 shortly after he broke his father’s pocket watch. From that moment, he decided there was a gap in the market for a collection of strong outdoor watches that were almost unbreakable.