Light's drawer trap

Light and Ryuk go to a department store where Light shops for supplies to construct a hiding place for the Death Note. Light reveals to Ryuk his new Death Note hiding place in a secret compartment under his drawer. Light inserts the drawer he made into the top right side of his desk.

Appearance
It has a key lock to lock the drawer in place and Light intentionally leaves the key in a lock because it was the most noticeable place he could think of and he keeps a regular diary inside the desk.

The lock is to satisfy any one else's curiosity to why the drawer might have a lock on it and the diary is to distract most people so no one will continue to search the drawer for the death note.

Hidden compartment
The drawer has a hidden compartment which is for hiding the Death Note and it can only be safely accessed using one particular method.

Light unscrews an ink reservoir from regular ball point pen and he pushes it up into a small hole underneath the drawer to lift up the bottom of the drawer to find the death note hidden underneath a fake bottom.

Electric Current/Defense Mechanism
Even if someone figures out that there is a fake base, Light designed the drawer to fully prevent anyone from ever finding the Death Note completely.

Once the ink reservoir is inserted it acts as an insulator preventing the flow of electricity around the circuit. When the fake base of the drawer is put back, a piece of rubber also prevents the flow of electricity.

However, if someone were to try and force the bottom of the drawer open then the circuit would connect and that would ignite the gasoline contained in the thin plastic casing instantly setting the death note on fire. This would destroy all the evidence that light ever possessed a note book that can kill. If he was ever questioned he will just say that he was hiding the real diary so no one would see it. He thinks it will sound like a believable excuse because it's his personal diary.