Another poster pointed out that the alarm might also fail to sound, or maybe the switch didn’t actually work, so you need to check it anyway. On Boeing planes,

Another poster pointed out that the alarm might also fail to sound, or maybe the switch didn’t actually work, so you need to check it anyway. On Boeing planes, many automations such as TOGO typically have a corresponding physical counterpart - in this case, autothrottle slides the throttle controls upwards to indicate that the engines were asked to go to full power. There’s also the engine instruments which show the engines reaction to the requested throttle level. It’s not hard to know that it didn’t set the throttle to full power, but the pilots didn’t check or didn’t know to check. An alarm would help, but would also be another fallible automation to be relied upon.