Unknown phone connected on Bluetooth

As stated, in the Bluetooth Menu of your iPhone is a list of in-range devices you can connect to. In this case it sounds like there was one nearby, but you did not connect to it. Once you are out of range those devices will disappear. Nothing to worry about there or in terms of your iPhone’s security, any personal information or your device cannot simply be compromised by Bluetooth. If a Bluetooth connection ever were to retrieve your messages or calls, such as for CarPlay, you would need to give explicit permissions in addition to connecting. Also, a lot of times connecting nowadays requires you to enter or match a pin with the accessory you are connecting to.

Also turning off Bluetooth when not in use won’t do anything, and in fact has some downsides. Firstly Bluetooth when not connected to a device uses no power. Secondly when turned off certain features won’t be able to work properly, such as Find My or your Apple Watch nearby.

That can happen sometimes when nearby devices briefly try to connect. If it disappeared in a second and you didn’t pair it, nothing to worry about. Just make sure to forget any unknown devices and turn off Bluetooth when not in use.

An unknown mysterious device on the Bluetooth list? Here's how to investigate and remove it:

Check for Persistent Connection

1. Before taking any action, test whether the device stays connected when you move away:
2. Walk to another room with concrete walls or move at least 1000 feet away.
3. If the device remains on the list or reconnects, it may be linked to your Apple ID, iCloud, or another persistent pairing method.

Steps to Remove the Device

1. Reset Network Settings
   1. This will erase all saved Wi-Fi networks and Bluetooth connections, which can help remove the mysterious device:
   2. Go to Settings > General > Transfer or Reset iPhone > Reset > Reset Network Settings
   3. After the reset, reconnect to Wi-Fi and check if the device still appears.
2. Check for Third-Party Apps
   1. Certain apps—especially those related to audio, video, AirPlay, or Bluetooth connectivity—might be keeping the device active.
   2. Review installed apps and delete any suspicious or unused third-party apps related to Bluetooth.
   3. Restart your iPhone and check again.
3. Look for Installed Profiles
   1. Some Wi-Fi routers, Bluetooth accessories, or enterprise networks may install configuration profiles that allow persistent Bluetooth connections.
   2. Go to Settings > General > VPN & Device Management
   3. If you see any unknown or unnecessary configuration profiles, remove them.
4. Forget the Device Manually
   1. Go to Settings > Bluetooth, find the unknown device, tap the (i) icon, and select Forget This Device.
   2. If the device reappears, try resetting all settings (Settings > General > Transfer or Reset iPhone > Reset > Reset All Settings).
5. Check for iCloud-Linked Devices
   1. If you use multiple Apple devices, check if the mysterious device is one of them.
   2. Sign in to Apple ID Device List and remove any unfamiliar devices.
6. Reset Network Settings: Settings > General > Transfer or Reset iPhone > Reset > Reset Network Settings: Only network settings are removed.
   1. When you reset network settings, previously used networks and VPN settings that weren’t installed by a configuration profile or mobile device management (MDM) are removed. Wi-Fi is turned off and then back on, disconnecting you from any network you’re on. The Wi-Fi and Ask to Join Networks settings remain turned on.
   2. To remove VPN settings installed by a configuration profile, go to Settings > General > Profiles & Device Management, select the configuration profile, then tap Remove Profile. This also removes other settings and accounts provided by the profile. See Install or remove configuration profiles on iPhone in this guide.
   3. To remove network settings installed by MDM, go to Settings > General > Profiles & Device Management, select the management, then tap Remove Management. This also removes other settings and certificates provided by MDM. See “Mobile device management (MDM)” in the iOS Deployment Reference.
   4. Reset your Network Settings. Tap Settings > General > Reset > Reset Network Settings. This also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you've used before.
   5. 
7. If the issue persists, you can try resetting all settings on your iPhone. This will not erase your data but will reset all personalized settings to their default values. Go to Settings > General > Transfer & Reset > Reset > Reset All Settings and confirm the action. Note that you will need to reconfigure your settings afterward. All settings—including network settings, the keyboard dictionary, the Home screen layout, location settings, privacy settings, and Apple Pay cards—are removed or reset to their defaults. No data or media are deleted.
   1. Reset All Settings: Return iPhone settings to their defaults - Apple Support:- Return iPhone settings to their defaults
   2. You can return settings to their defaults without erasing your content.
   3. If you want to save your settings, back up your iPhone before returning them to their defaults. For example, if you’re trying to solve a problem but returning settings to their defaults doesn’t help, you might want to restore your previous settings from a backup.
   4. 
8. Make sure you have the latest updates installed.
   1. Update Over-the-Air (OTA) —> Update your iPhone or iPad - Apple Support (IN)
   2. Update using iTunes/Finder —> Update your iPhone, iPad, or iPod touch - Apple Support (IN)