Gammon my buddy!!! You live in these forums ;)
Well, the xbee ZigBee is waiting for an interrupt to wake up.
So here is my theory. The xbee consumes about 34mA when its on. The xbee takes 50ms min interval to read its first ADC or any sensor value. That doesn't include the time it takes for the sensor to finish its rise and fall time. Even though the sleep current is lower, the time required to be awake and the power it uses does not make the xbee a standalone coin cell alternative. I would like to poll a sensor every few seconds. Almost real-time data. And if the threshold I need is tripped, then it wakes the xbee and sends the value.
So arduino is using its internal wdt and wakes up in x seconds. Reads the sensor. Goes to sleep. When threshold is hit, arduino wakes up the xbee and sends the recommended packet to the main hub.
At the moment I am at 5.2-5.4uA with xbee sleeping. Arduino is currently using 4.5uA by its self. I will also use a pin interrupt on the adduino using a Reed switch in case a door opens or closes. That would be real time sensing passively.
I'm using a 3.3v ir sensor made by sharp. It uses around 24mA. Is there a better. Cheaper. Smaller option to detect an object at around 5 feet? Ultrasonic is large, expensive and rise fall times are too large.