Unusual battery drain
Phone getting hot when not in use
Strange background noise during calls
Calls dropping or echoing unexpectedly
Delayed shutdown or startup
Unexplained data usage spikes
Random restarts or crashes
Text messages appearing sent or read when you did not do it
Unknown apps installed
Settings changed without your action
Microphone or camera indicator appearing unexpectedly
Contacts, photos, or files missing or altered
Receiving odd SMS codes or verification messages
Hearing clicks, static, or interference on calls
Phone behaving strangely only in certain locations
Account logins or password reset alerts you did not request
Friends reporting strange messages from your number
SIM card issues or service disruptions
Device management profiles or admin access you did not approve
Security apps reporting spyware or malware
Carrier account changes you did not make