Arduino and xbee sleep question

Hey everyone, I have saw a few post about the xbee and arduino having a sleep mode. My question is, is this a default mode? Will an atmega328 and an xbee series 1 or 2 automatically go into sleep mode after an pre-determined amount of time? If so is there a way either through software or hardware that will prevent the xbee and atmega from going into sleep mode? The reason I am asking this is I am working on an alarm system using a pir motion sensor and a series 1 xbee network communicating back to a "control box" in another room that sets off an alarm if motion is detected. While function testing the project It seems to work perfect and so I will left it on all night but the next morning setting off the PIR sensor does not register back at the control box. I have just begun investigating what is causing this issue as I have had another project keeping me busy but I wanted to check on this issue with a sleep mode first and see if that is what is causing a problem.

Thanks in advance

No, modes are entirely up to you to program...

So "out of the box" neither the xbee S1 or the arduino should be going to sleep?

jeremydial1981: So "out of the box" neither the xbee S1 or the arduino should be going to sleep?

Correct.

Ok, sounds great. Thanks allot guys.