TL;DR: Stalkerware tends to show up as constant background data use, the phone staying warm even when you're not using it, faster-than-usual battery drain, and unfamiliar accessibility or device-admin permissions granted to an app you don't recognize. Check Settings > Accessibility and Settings > Apps > Special Access > Device Admin Apps (Android) or Settings > General > VPN & Device Management (iPhone) for anything unrecognized, uninstall it, change your passwords from a different device, and if you believe you're being monitored by someone who could see you take these steps, consider using a safe device and contacting a support organization first.
Stalkerware tends to show up as constant background data use, the phone staying warm even when you're not using it, faster-than-usual battery drain, and unfamiliar accessibility or device-admin permissions granted to an app you don't recognize.
What Usually Causes This
This software is typically installed by someone with brief physical access to the device, disguised as a system utility or hidden behind an innocuous-looking icon, and configured to run silently in the background.
What to Do About It
Check Settings > Accessibility and Settings > Apps > Special Access > Device Admin Apps (Android) or Settings > General > VPN & Device Management (iPhone) for anything unrecognized, uninstall it, change your passwords from a different device, and if you believe you're being monitored by someone who could see you take these steps, consider using a safe device and contacting a support organization first.
If this looks similar to something else you've seen, it's worth reading How to Check If Your Smart Home Devices Are Secure.
This pattern shows up elsewhere too — see How to Check If Your Smartwatch Is Leaking Data.
Frequently Asked Questions
What are the real warning signs?
Stalkerware tends to show up as constant background data use, the phone staying warm even when you're not using it, faster-than-usual battery drain, and unfamiliar accessibility or device-admin permissions granted to an app you don't recognize.
What usually causes this?
This software is typically installed by someone with brief physical access to the device, disguised as a system utility or hidden behind an innocuous-looking icon, and configured to run silently in the background.
What should I do about it?
Check Settings > Accessibility and Settings > Apps > Special Access > Device Admin Apps (Android) or Settings > General > VPN & Device Management (iPhone) for anything unrecognized, uninstall it, change your passwords from a different device, and if you believe you're being monitored by someone who could see you take these steps, consider using a safe device and contacting a support organization first.
Should I be worried if I only see one sign?
One sign alone (like a slower device) is usually not cause for alarm — most single symptoms have mundane explanations. Multiple signs together, especially unexpected data usage or unfamiliar apps, are worth investigating.