"Well, then, I must make some suggestions

"Well, then, I must make some suggestions to you. When you sat down on that chair yesterday, did you do so in order to conceal some object which would have shown who had been in the room?"

Bannister's face was ghastly.

"No, sir, certainly not."

"It is only a suggestion," said Holmes, suavely. "I frankly admit that I am unable to prove it. But it seems probable enough, since the moment that Mr. Soames's back was turned, you released the man who was hiding in that bedroom."
optical transmitter
bathroom hand dryer