Apple - Why does my iPhone alarm go off one hour late?

I believe you’re a victim of the iPhone time bug. You don’t specify your iPhone model nor iOS version, but I’m sure you have the above mentioned problem:

Reports from around the world have exposed a daylights savings flaw in the iOS software, which is causing alarms to go off either an hour late or early, depending on where you live.

Google for more love in the subject.

I ran into the same annoyance myself, and stumbled into this workaround:

Edit the "Repeat" setting for your alarm, and set it either to "Every day" or "Never". Now the alarm goes off when it should, unlike when it's set to e.g. "Weekdays". Here's a screenshot — green works and red doesn't:

For more background info, I recommend these MacRumors articles:

• iOS 4.1 Daylight Saving Time Bug Strikes Europe
• Apple Support Acknowledges iOS 4.1 Daylight Saving Time Bug

The latter post contains Apple's recommended workaround (same thing as above, but with some additional information):

To resolve this behavior for existing alarms, set the repeat interval to Never. You will need to reset these alarms for each day you need them.

After November 7th, 2010, you can set your alarms to repeat again.

It's now past November 7, and I just verified alarm works correctly again, even if repeat is set to e.g. "Weekdays". Which is nice. But I hope they fix the bug once and for all before the next DST shift occurs!