The Control Center remote has an accelerometer built in. In order to enhance the battery life, the remote goes to sleep when it is stationary. Even slightest movement of the remote (picking it up, for example) wakes up the remote.
Expert tip: The remote will not control the main unit when it is sleeping. If you try to use it on a table, after it has been sitting for a while, the remote will likely not respond until you wake it. Just give it a small shake or pick it up before use.