How to know if someone has opened your door while you're gone?

How one can set something up that would indicate someone had opened your front door?

Here are few simple tricks you can do:

• Put a small hair between the door and the frame, but visible so it is exposed slightly outside.  If you can see it is dislodged already, the door has been opened.  If not, then it has not.

• Get a small piece of paper and tape it to your door or door frame, in such a way that you can put it in a position.  When the door is opened and closed again it goes to a different position.

• Put something very close to the door. but just close enough so the you can slide thru the door without moving it.  If he opens it completely the object will be moved.

• Get security camera with motion detection.

The last option is the most expensive one and I would consider it as the last resort. 

I hope you try this useful tips at home.