Date: 201910
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737 Next Generation Undifferentiated
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Security
Detector: Person Flight Crew
When detected: Pre-flight
Result: General Flight Cancelled / Delayed
Contributing factors: Procedure
Primary problem: Procedure

Narrative: FO (First Officer) noticed [a suspicious] device hanging on spare bulbs panel before push as he was plugging in his personal headset. Contacted Operations and asked for jet bridge return with a GSC (Ground Security Coordinator). Looked up previous pilots and discovered they were at Gate XX. We reviewed QRH. Called Gate XX and confirmed device was previous FO's. Ownership was identified. Previous FO said device was battery pack for their personal headset. Device given back to previous FO by GSC.


Second narrative: While getting ready to close up cabin door I turned around to plug in my headset and noticed a suspicious item hanging from the spare bulbs handle. I uncoupled it and inspected it; noticing an 8 cell battery pack similar to those used in remote control vehicles; attached by a zip tie and wired in to a black box that had a 2 position switch; led light and what appeared to be an antenna jack. I showed it to the Captain who quickly tried to get the Gate Agent as she had just closed the door. I called Operations requesting the jet bridge be returned and the Captain also asked for a GSC (Ground Security Coordinator) which I asked for through Operations.I looked up the inbound flight and the crew list assuming it was the previous First Officer's homemade charging device but also realized this could be an actual threat so we placed the item on the center pedestal and left it alone. The door was opened and the Captain asked our Gate Agent to contact the Gate Agent at Gate XX where the previous FO (First Officer) was.We reviewed the bomb on board QRH as well as threat level 3 in the FOM. The Captain then went into the jet bridge with the device and handed it over to the GSC. Shortly after; the previous FO came down our jet bridge and confirmed ownership of the suspected device and explained it was a battery pack for his headset.The GSC gave the device to FO who apologized for the confusion. The GSC confirmed the Captain and I felt the aircraft was secure and we were both ok to continue the flight and there was no need to deplane the aircraft. We both felt the aircraft was safe and the device's ownership was confirmed and no threat existed. We boarded the aircraft; ran the remaining checklists; and departed a little past departure time. We were able to make up most of the time and got the customers safely and comfortably to [the destination airport].


Synopsis: B737 NG flight crew reported a suspicious device hanging from the spare bulbs panel resulting in a flight delay.