At the top of the door you can make a small hole so that the container in which some jewel will be stored in it.
In the photo as a container used a cigar case. It is attached to it a metal washer for easy removal of the container from the cache magnet.
Homemade cache - STEP 1:
Homemade cache - Step 2.:
Homemade cache - Step 3.:
Homemade cache - Step 4.:
Everything! Homemade door cache is ready!