How can I check whether an app is using my camera or microphone?

Reviewed answer

Check the device's activity indicators and permissions; a light alone does not prove spying.

On iPhone, open Control Center to identify recent camera or microphone use. On Android, check Privacy dashboard where available.
Review camera and microphone permissions and remove access from apps that do not need it.
On Windows, search Settings for Camera and Microphone. Close unexpected apps and use a built-in camera shutter if available.

Get help if

An unfamiliar app uses these features repeatedly, or activity continues when you cannot explain it.