Unexpected sound played on iPhone

OK... someone logged into your iCloud account at https://icloud.com/find or a family member in your apple family sharing group used find my to play a sound on your phone in an attempt to locate it.

If it wasn't initiated by you or a family member, you need to change your Apple account password NOW!

Sorry, but I can't read Russian and to think anyone here on this user to user only forum could possibly guess what sound played on your phone or from where, isn't possible. I do see that your phone was beyond out of charge. It could have been a warning that your phone needed to be charged. You should NOT let the battery dip below 20% or EVER let if fully deplete. Doing so will prematurely age your battery faster, shortening its useful life.

Instead, you should be putting your phone on its charger when you go to bed at night and leave it on the charger with Optimized Battery Charging enabled. You can put the phone in a Focus Mode to avoid being interrupted when you're sleeping.