Thanks for your responses.
Bit more of a background - my (portable) device needs to be powered for only maybe 20 seconds every ten or twenty minutes, and I'm aiming for a lifetime (before the batteries need to be changed) of a few months. Subsequently, I need the "off" state to draw no more than 100uA, perhaps even less. If I use the Arduino as is (which is my preference), I'll need to design a circuit that switches the power on and off at required intervals. I've been playing around with the DS3234 RTC, which has an alarm setting built it. I think the RTC draws 120uA which may be bareable, provided any other additional circuitry doesn't draw too much more current. The DS3234 provides an interrupt low signal when the alarm triggers.
The alarm set into the RTC will trigger when the device needs to turn on (ie, every ten minutes), and somehow the Arduino will need to power down after the device. Given the potential problems associated with powering down the Arduino at random, it may be best to initiate a reset each time I turn it on.
So the basic operation would be:
1. RTC time and alarm set
2. Arduino starts up, runs main program
3. When program finished (after ~20 seconds), Arduino powers down
4. RTC alarm triggers at some future time (ie ~10-20 minutes later) and turns the Arduino back on
5. Arduino resets itself to ensure peripheral devices don't latch up (as per Grumpy Mike's suggestion)
6. Back to step 2, process repeats...
The RTC will be powered directly from the battery, but I will also need some kind of switch to switch the power to the Arduino (switching ON when the interupt pin from the RTC goes low; and switching OFF when a signal is sent from the Arduino). Obviously this needs to be low power.
I came across this Pololu switch circuit: http://www.pololu.com/catalog/product/751/resources
It can cut the power when it receives a high signal, but not the other way around. The physical (push button) switch in the circuit can switch the power on and off when the switch shorts.
Can anyone suggestion a possible low-power (ie uA) solution that can switch the power on (via Arduino) and off (via the RTC)? Or a way of adapting the pololu circuit?
Any suggestions would be much appreciated!