EMB ERJ 170/175 ER/LR
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Time Pressure; Situational Awareness; Confusion; Distraction
Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown
General None Reported / Taken
Human Factors
Held off starting the APU; since there was no need for it until departure. Once the door was closed; I started the APU; but the weak GPU meant a lot of systems temporarily tripped off line. As things came back online; I noticed; among other things that the BAGG (Baggage) SMOKE light was on. Having previously dealt with that light coming on due to a power spike; I reached up to simply reset it by pressing the test button; but in a moment of confusion; I instead reached for the BAGG EXT button; which of course; set off the cargo bay fire extinguishers.The FO (First Officer); unaware of my action in the moment; since he had been getting his checklist ready; was alerted by the EICAS warning; BAGG SMOKE; and pulled the EPC (Emergency Procedure Checklist). We proceeded with that to make sure everything had subsequently been actioned accordingly. Ops was notified; so they emptied the cargo and checked the bags of those pax (passengers) who chose to continue with our flight. In the meantime; I called [Operations Control] and [Maintenance Control]; and we processed an MEL for the BAGG EXTBTL INOP. Once pax and bags had been processed; the flight continued.Ultimately; it comes down to just pushing the wrong button. Contributing factors and distractions were:-When the door was closed; we realized the ground air was still hooked up; because there was a significant pressure bump in the aircraft.-At the same time; I was just about to start the APU; but we were distracted by the pressure spike.-We also noticed that the jetbridge was being pulled back; which caused us concern about the GPU still being hooked up until we realized that the GPU was a portable cart; separate from the jetbridge.-When the APU was started; all of the displays went dark for a moment due to the weak GPU; and we had to look over everything as the power came back on to see what needed to be reset; etc.A hard reminder of the lesson to not even touch a control; switch or button until you've paused; even for the briefest of moments; to reconfirm that it's the correct control and the consequences thereof.
ERJ flight crew reported inadvertently activating cargo fire extinguisher at gate.