Remember this... your fobs are transponders, little CB radios, phones, whatever works for you to understand two way communications.
When the vehicle is turned off, those comms continue with all fobs in a specific range based on how Honda engineers placed antennas to read them. The signal and expected decay of a zone outside the vehicle sets off the first beep once all doors are locked. This happens only if that signal drop off meets certain thresholds compared to the model programmed in vehicle memory. They know what a fob looks like walking away really slow and fast within preset times and tolerances. In other words, some distance sensing is used and there’s timing involved (I lost you in an ok way or not so ok way but just in case I’ll wait a little in case you pop up again). This is the lag between first and second beeps if you stand near back row door. In a Honda tent video, Pro Jason demonstrates the built-in pouch inside tent aft of the gas fill is outside fob detect range so truck stays locked with key there zipped in with you.
If the vehicle can’t discern fob signal due to noise from any kind of RF interference, most commonly a phone but not necessarily from one of its primary transmitting frequencies, it could be an intermediate freq one (think of one signal made by an oscillator in your phone produced or mixed with another to produce, decode, or modulate another signal). It is possibly a harmonic of a phone frequency causing this interference.
The most likely cause of the chirps that mimic door not shut completely are, can you guess the obvious?
The OTHER transponder fob you may have on your key ring!
Don’t get hopes up thinking this is a fixable quirk. My ‘17 does this about weekly and this happened AT the dealership service bay when dropping it off for the Fuel Pump Recall. I’d had it in for just this issue with and without scheduled service before. TWO service writers stopped and turned saying they do that, there’s nothing we can do before I could ever say, there, you can’t CND it now. I was a bit shocked but quickly said, how about we have a bigger problem as they all do that doesn’t make it right!
I’ve learned to open and close any door or wait more than 8 seconds in range then try again.