Flight Crew Private; Flight Crew Instrument
Flight Crew Last 90 Days 8; Flight Crew Total 1800; Flight Crew Type 1600
Communication Breakdown; Human-Machine Interface; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Environment - Non Weather Related; Human Factors
Landing after the second flight of the day; during shutdown noticed that transponder had been left on the previous flight's code assigned for flight following instead of having been set to XXXX which would have been appropriate for this flight conducted without flight following. The transponder is ADS-B; so there was still a unique identifier. The flight originated at ZZZ shortly after XApm when the Tower had shut early due to COVID. I am used to getting a flight following code from ZZZ ground; but did not this time because of the closure. Had I been at a normally uncontrolled airport; I would have followed my checklist for electronics; but I am so used to getting codes at ZZZ that I did not pay proper attention to that portion of the preflight/runup. Compounding this is that the transponder is new and less familiar than the one I have flown with for years; which actually would indicate more attention is needed. Always run through full electronics checks on startup and shutdown!
GA pilot reported inadvertently leaving the transponder code set from the previous flight. The pilot was accustomed to getting a code from the Tower; however the Tower had closed early due to COVID-19 hours and the pilot did not check the transponder.