As a consequence of yesterday's fiasco, we set no fewer than 3 alarms last night - the unreliable alarm clock, plus the alarms on both our mobile phones. Two of these went off as expected - I cancelled the third before it also did its job.
Unfortunately, though, the consequence of not really trusting the alarm clock was that actually getting to sleep was rather difficult. So, any benefit that we might have derived from those two hours of extra sleep yesterday were lost overnight. Which is not quite ideal.
Meanwhile, as a result of this we've concluded that the time has come to ditch the current (unreliable) alarm clock and replace it with a 'real' alarm clock. Which is probably a long-overdue step. My inclination at this point is to go for a "sunrise lamp" device, which should help with those dark winter mornings, though this is by no means fixed.