Alarm volume decreases at night

If your iPhone’s alarm volume is decreasing on its own, there are a couple of settings you should check before assuming that it is a software issue.

1. Check Shortcuts Automations:

Open the Shortcuts app, tap the Automation tab, and review your existing automations. Check whether any automation is configured to change the volume at a specific time, when you go to sleep, when you wake up, or when a particular Focus mode is enabled. If you find one that changes the volume, modify or disable it as appropriate.

2. Check “Change with Buttons”:

Go to Settings > Sounds & Haptics > Ringtone and Alerts and check whether Change with Buttons is enabled. When this option is turned on, the volume buttons can change the Ringtone and Alerts volume, which also affects your alarm volume.

If you want to prevent the alarm volume from being accidentally lowered using the physical volume buttons, turn off Change with Buttons. You can then set the desired Ringtone and Alerts volume using the slider.

These are two important things to investigate if you notice that your alarm volume is getting lower without you intentionally changing it.

If you feel an unauthorized person/app is remotely using, controlling or monitoring your device, then that is possible only if you have done one or more of the following Don'ts...

1. Don't hand over an iPhone to kids or to a stranger without Enabling Guided Access
2. Don't share Apple IDs
3. Don't Jailbreak
4. Don't share sensitive information pertaining to your device
5. Don't give in to Phishing
6. Don't plug in your device in Airports and Public places through third-party cables and trust the device. Beware of Juice Jacking. (Especially in India)
7. Don't leave your iPhone unlocked and unattended in public places like offices, schools, malls, etc.

If one of the above is true then quickly change the Apple ID Password and Return iPhone settings to their defaults.