A319 First Officer describes his perspective of an inadvertent slide deployment; from his seat watching the ECAM door page.

Narrative

The gate agent entered the flight deck and verbally stated the passenger count and left. The 'C' Flight Attendant then entered the flight deck and asked the Captain if it was okay to close; to which he responded yes. At this time I was listening to the hourly ATIS update and the weight and balance message was printing over the ACARS. I just happened to glance down at the lower ECAM Door page and noticed that all doors were closed with only the over wing exit white slide lights illuminated and the 1L door white slide light illuminated. I then heard a noise that sounded like it was coming from the 1L door entry area; at the same time I looked down at the lower ECAM Door page and saw the 1L amber cabin door light illuminated along with the 1L door white slide light illuminated. I immediately notified the Captain; who immediately left the flight deck. He then came back and reported to me that the slide had been deployed from its housing. Operations were then notified and Maintenance requested. I'm not sure as to how this event happened since I never saw the events taking place outside of the flight deck.