Electronic Geocache Power Saving

I built an electronic geocache on my development board: if you flash a correct morse code sequence on a light sensor, it gives you (in morse code with a led) the coords of the cache. It works really nice! What I haven't figured out is how to save power, as this will run on a battery outdoor somewhere in the woods.

The program constantly polls the LDR sensor. If this value exceeds a treshold (= a flash is detected), it starts executing the code associated with checking the Morse code.

What are according to you the best ways to make the power consumption for this project as low as possible?

From this: http://gammon.com.au/power I conclude:

  • build a bare bones arduino setup (no development board)
  • interrupts won't work, because I don't have a low, high, rising or falling trigger, only an analog light sensor as 'trigger'
  • the watchdog timer set to a short interval like 8 ms is my best power saving option?

thanks!

What's your light sensor? Could you replace it with a small photovoltaic cell that can be left unpowered, and just generate enough of a pulse to trigger an interrupt to wake up the Arduino? If you can replace the light sensor with a mechanical switch, even better: you can turn the Arduino on, and design it to turn itself off after a few seconds of inactivity.

the light sensor is a simple light dependent resistor in series with an other resistor, creating a voltage divider. This is read into the arduino as an analog light value and compared to a certain treshold

So, how about replacing it with a PV cell that can generate enough power to trigger an interrupt on the Arduino?