hmmm...good idea with waking up the mcu with external pulse. But I am afraid this can be used only for "few-pulses-for-a-day" cases only if I want my node as low power and battery powered. For ex. if there will be 10 pulses to a minute, the node will drain too much.
So maybe some cmos counter IC can be a good solution?
If you manage the hardware properly, you can easily handle 10 pulses per minute without substantial power drain. The trick is to have all other hardware powered off, use the MCU as a counter and immediately go back to sleep after each pulse.
Example:
Assume 7uA MCU sleeping, 8mA when woken to count the pulse, time awake=1mS, interval between pulses=6seconds, your average current will be 8.3333 uA if this condition was continuous 24/7. Note that the 'awake' average power is only 1.3333uA in this case. At 8.3333uA continuous drain, a pair of AAA batteries would give you about 17 years of life if Murphy didn't throw other problems at you (like corrosion, etc).
Now, obviously you'll want to send this information at some point, but if you keep that duty cycle low (once every ten minutes, once every hour, etc) then your device will still last years on a couple of batteries.
Tom
PS: You can use LPL's nifty neat new timer breakout to power up the radio and any other devices you need on a periodic basis for reporting the data. It can also wake the MCU, and, with this wake up, the MCU initializes the radio, sends the report, and turns it back off and goes to sleep.