Have you used a multimeter to see just how much current the arduino is drawing?
yes - see my original post at the top
What is the microcontroller doing in this application?
Well I'm new to this stuff. I started out looking at X10 devices. The sensors seemed OK but I couldn't find the display panel I wanted. I stumbled across Arduino and thought they be good to let me customize my display of things. Then rather than trying to get an X10 RF receiver interfaced to an Arduino I thought just to use Arduinos for the sensors too. :-/
A stand-alone XBee could easily give a few years on 2-AA cells.
Wow thats great if it's an option ;D I had come across an XBee as just a way to get wireless comms from one Arduino to another. Because they were a bit expensive I've actually been using the cheap RF transmitter & receivers that are available. I've got a basic reed switch setup from Arduino to Arduino using these, but my issue I'm seeing now is the lifetime of the batteries to power the remove sensor.
Do you know off hand which is the cheapest XBee unit I'd need to be able to use it to send door open/close messages back to a base Arduino (with a mounted XBee), noting I'm planning to have several (< 10) monitoring points transmitting back to the base. I see there are quite a few options for them at: http://www.sparkfun.com/commerce/categories.php?c=111&sidx=retail_price&sdir=ASC&sipp=100&x=0&y=8