fail–safe 
/ˈfeɪlˌseɪf/ adjective
/ˈfeɪlˌseɪf/ adjective [more fail–safe; most fail–safe] : certain not to fail
▪ Of course, no system is entirely fail-safe. ▪ He was looking for a fail-safe source of money. ▪ a fail-safe device/mechanism [=a device/mechanism that will not break]
▪ Of course, no system is entirely fail-safe. ▪ He was looking for a fail-safe source of money. ▪ a fail-safe device/mechanism [=a device/mechanism that will not break]
