I a a diabetic and have several alarms set to remind me to take glucose readings, insulin, carb intake etc... So I have several alarms set to remind me.

I have been away for 3 days. Yes that's 3 days. I forgot to take my damn charger. Anyway, the battery lasted 2 days as I turned off all comms. Finally the battery run out and the n900 shuts down. Weird bong sound and all. Everything off. All dead.......well not quite......the bloody alarm is still active which is great but the screen does not respond to turn the alarm off. You cant turn the alarm off damn it.

So, I ended up pulling the battery out. But....

I put it back in and guess what? Yup, the bloody alarm resumed. I just got home after 24 hours of this damn alarm going off every 10 minutes cos I cant turn it off and short of leaving the flipping battery out of the unit, it just wont stop beeping and I cant turn off.

As I said I just got home, so I put it in the charger. After an hour the system auto booted and finally I was able turn the alarm off.

So, my question.......when the system is off, is it really off? If it is then is the damn alarm running out of nvram on a different processor or something. Damn weird setup to me. But I tell you, the system had fully shutdown, I could not boot t as the battery was dead. But the bloody alarm, lives! Go figure.

The system shuts down at 3.2Volts on the main battery. The hardware cutoff is at around 2.8 iirc, so there's a small amount of power left.

The clock is always running, there's a separate backup battery for it. The clock will switch the device on for alarms.

The alarm working when the phone is off is a normal (at least for every phone I've had so far) and also desirable (in my opinion) thing. If the battery is too low for the phone to be able to receive touch screen input, it might be annoying in rare cases (like yours), but still this "feature" is a good thing. The alternative would be that the alarm doesn't work when the phone is off, which is definitely not good.
A possibility would be for the alarm not to work when the battery is too low. I'm not sure though how useful that is. Even if it might be slightly annoying I'd prefer my phone to wake me up even when it's almost out of battery, even if I can't turn the alarm off.

This has only been the case for all the nokias I have owned. Its really great when you want to conserve battery but still need to be reminded of something.

i agree with the it's a good thing opinion, but... maybe by adding a way to turn the alarm off with hardware buttons like the "lock screen" slider or something may be a way out in the situation described by the OP...

Hmmm...
As I said, I think its great that the alarm goes off even if your battery is dead. But not being able to turn it off in any way except pulling the battery out is maddening. Because you cant turn the alarm off, it times itself out....only to start again 10 minutes later. AAaaaarrrrrgggg! Try putting up with this all day and believe me, the River Mersey starts to look very like an n900 repository.

In short: This should not happen.
In reality: This has happened to me a few times too. It's a bug.

There should be a way to stop or snooze the alarm also with qwerty-keyboard, I think.

Like ENTER for stop and SPACE for snooze.

OP could file a bug report.

Hmm... makes sense. Is it a standard RTC chip with a limited number of hardware alarms, then or something more complicated? I have at least on one occasion set a good 25 or so alarms on the N900, and I haven't ever reached a hard limit in software. Any info? (A datasheet link would be excellent, if you have it handy - or an IC #, for that matter)

On the topic of annoying alarms, though, my dumbphone takes the cake with that, I think. You can only dismiss an alarm (e.g. without manually unsetting it in the config) when it is ringing, and not when it's snoozing in between rings. This would be fine, except that it will only snooze a certain number of times before turning off entirely. That would be fine, except that in that case, while the config says the alarm is disabled, it actually isn't, and will ring at the same time the next morning unless you manually set it and unset it all over again. :/ *sigh* Also, when ringing, the modal alarm dialog covers the system clock, and only displays the time when the alarm started ringing - so if you sleep through a few rings, you might well think it was half an hour earlier, and be late... </rant>

So... if i put my alarm on for work and turn my phone off i'm safe to go to sleep and the alarm will still go off?

Not tested that yet past phones did it which is great because people seem to think its funny to ring me at 3am when drunk when i have work in the morning..