Call the airline ahead of time and ask about their policy concerning metal detectors on their planes. While most will be okay with you bringing it, especially if it's a smaller hobby metal detector, it's better to be safe than to risk having to leave it behind at the gate.
Buy travel insurance if you are traveling with several expensive metal detector models. Therefore, if they get lost, you will get reimbursed for what they were worth.
Purchase a hard case to put your metal detector in. This hard case should have minimal room for your metal detector to move around inside. Put your metal detector in the center of your suitcase if you don't have a hard case. Then, surround it with clothes, bubble wrap, or and other soft items to protect it. Make sure you can get to it quickly at the gate in case security asks you to remove it.
Try to find a case for your metal detector that locks. Whether it's a hard case or just a suitcase, your metal detector will be more secure if it's locked. Also, be sure unlock your case or at least have the key ready before you pass through security.
Check the case that your metal detector is in with your luggage. Avoid carrying it on the plane as a carry-on.
