How do you tell if someone entered your apartment and can I place something on the door or its frame to tell me this?

Answer 1

see this http://answers.Yahoo.com/question/index?qid=20081122140846AA3Ff82

Thank you, that link has a collection of some good answers to my question.

But most of those answers rely on something that can be seen by an intruder, like a piece of tape on the outside of the door, a piece of tape the intruder could replace when leaving.

Is there a way to tell if the door has been opened and know for certain that the intruder did not notice it?

The laser alarm answer is good, especially if it could be arranged so that the alarm does not go off, and a counter indicates if any people and how many people crossed the laser's path. (If you live in an apartment building like me, you don't want the alarm going off for a long time as it would get the other tenants and the manager very upset.)

Another problem with electronic devices such as a hidden camera and the laser is that there are sensors that can detect these electronic devices, and some of these sensors can even turn off the devices or at least point you to where they are.

Are there any hidden cameras including IP cameras that cannot be detected in any way?