I did have my charger plugged in without being plugged into an outlet. I can’t be sure if the alarm stopped after the charger was disconnected from the phone. The port and the cord weren’t hot.
A random alarm went off for no reason on my phone. It was 4 minutes before a scheduled alarm at 1230. There was no notification and no way to turn it off. It just went off on its own after about 5-10 seconds. The sound reminded me of the old digital clocks from the 90s that had a really obnoxious alarm if you decided not to wake up to the radio.