His face indicated that he was puzzled. In his hand he was holding a disk that was something like the flat telephone receivers one sees often on interior office telephones. To it was attached a rubber tube like that which Kennedy had picked up in the office a few minutes before.
“My man found this thing on the roof below,” explained Burke, with a look of inquiry. “What do you suppose it is? How did it get there?”
Kennedy took the disk and began examining it carefully, fitting on the other rubber tube.
“Perhaps it had served its purpose—was no longer of use,” he meditated. “At any rate, if some one had to get away with that telautomaton he would not want to burden himself with anything else that was unnecessary. He might very well have discarded this.”
What the thing was I could not imagine. We all crowded about, examining it, not even Burke offering an explanation.
Suddenly Craig’s face lightened up. He thrust the tubes into his ears and walked over to a smaller safe that was still locked. As he turned the combination handle he held the black disk up close to the safe. The intent look on his face caused us all to watch without a word. Around and around he turned the handle slowly. Finally he stopped. Then, with a few quick turns, he gave the door a pull and it swung open on its oiled hinges.
We fairly gasped. “What is it?” I demanded. “Magic?”
Kennedy smiled. “Not magic, but black science,” he replied. “This is a burglar’s microphone.”
“A burglar’s microphone?” I repeated. “What’s that?”
“Well,” he explained, “the microphone is now used by burglars for picking combination locks. When you turn the lock a slight sound is made when the proper number comes opposite the working part. It can be heard by a sensitive ear, sometimes, I am told. However, it is imperceptible to most persons. But by using a microphone it is an easy matter to hear the sounds. Having listened to the fall of the tumblers, the expert can determine what are the real numbers of the combination and open the safe. That is what happened in this case.”