Any recommendation how to keep to a very minimum usage of battery for an Arduino board that will be powered by battery and monitoring door open/closed status (use of magnetic reed switch for detector & RF transmitter using virtualwire library).
For example: a) should I use polling or interrupt (I assume an interrupt would be better)? b) if using an interrupt what best to do in the main loop? e.g. put a long delay? nothing? c) anything else I should do in the setup() method to help reduce power usage?
Some notes: i) I was assuming I'd use a 9V batery ii) I'm using the "Arduino Pro 328 - 5V/16MHz DEV-09219" http://www.littlebirdelectronics.com/products/Arduino-Pro-328-%252d-5V%7B47%7D16MHz.html. This seemed to be the cheapest board for what I need (?)