How do I know if Authorities are monitoring my device?

I need to know if the authorities are monitoring my android device.

Welcome to Android Central! Why are you worried about this? Are you doing something the authorities would be interested in?

usually they would know how to hide their tracks

"The authorities" don't have to monitor your device, they can just get a listing of numbers you've called, sites you've visited, etc. With a warrant in those countries that have real laws, without one in countries that don't.

If you never want "them" to know what you're doing, live in a cave in a jungle, and never use anything that uses electricity (or batteries). Otherwise, everything you do leaves a trail.

What Rukbat said. You won't know if they are. They could just go to your carrier and see your records there.