Hand protection has gone through several iterations before the new generation of self-checking
, ergonomic, optical touch-buttons.
Simple circuit buttons wired in series began to be used for machine activation. The operator had to push and hold down the buttons. This method was easily defeated by operators who tied down one button and used the other to restart the machine.
Newer actuation devices are true safety systems as they use redundant forced-guided contacts and monitoring to assure that faults will be detected and the machine will fail to safe.