B737-800 Flight Crew reported that a gate agent and assistant attempted to open an armed aircraft door from the outside after noticing a jetbridge temperature probe cord protruding from the door. Flight Attendants prevented an inadvertent escape slide deployment.

Narrative

After the boarding process was complete; the gate agent closed the L1 boarding door. After the door was closed; the agent noticed that the jetbridge temperature probe was still in the aircraft as the cord protruded from the aircraft door frame. Without notifying the flight attendants; the agent and another assistant attempted opening the L1 boarding door from outside the aircraft. At this point; the L1 boarding door had been armed as per normal procedure by the FA A with the 'flag' in place. Both the A and B FAs recognized that the armed door was being opened by the agents and immediately reacted to prevent it from being opened. The FA B grabbed onto the door handle and pulled on it to prevent the door from being opened. Simultaneously; the FA A rushed to disconnect the girt bar to prevent the slide from deploying. By their quick actions; both the FA A and FA C prevented an inadvertent slide deployment and potentially a fatal mishap.Cause: A late night and delayed departure may have contributed to overlooking the removal of the jetbridge temperature probe. Rushing and complacency from the agents definitely led to the task of retrieving the probe without properly notifying the flight attendants to disarm the door prior to re-opening.