Abstract: An object of the present invention is to provide a keyway plug for preventing the correct key from opening a safe deposit lock. Another object is to provide a keyway plug that is hidden inside of the lock and out of view from the public. The keyway plug of the present invention provides a means for preventing the correct key from opening the safe deposit lock, while overcoming the deficiencies of the prior art. It includes a plug, an insertion device and an extractor. The plug fits into the keyway to block the entrance of a key. Its tip is similar to the tip of an ordinary safe deposit key. The plug is properly seated in the keyway by an insertion device. Unlike the plug of the prior art it does not protrude from the lock and is not visible from casual inspection. An extractor is used to remove the plug from the keyway. The extractor includes a magnet which is concealed under the head of the device. As the extractor is inserted into the keyway and makes contact with the plug, the plug becomes magnetized.