Prox-based limit switches provide a simple, modular alternative to custom sensors used in mistake proofing, or “Poke-Yoke,” initiatives. ProxPlunger and WeldSwitch devices use spring-loaded pins and buttons to determine if parts in process are present and/or properly situated for the next step in a process (e.g., welding, painting, etc.). Steel and copper-steel alloy construction are available. Stock and custom designs are offered.