“What is it?” I hastened to ask, looking curiously at the oak box which contained still everything except the tiny black disc and the wires leading out of the window from it and from the new telephone transmitter.

“This little instrument,” he answered slowly, “is much more sensitive, I think, than any mechanical or electrical eavesdropper that has ever been employed before.  It is the detectaphone—­a new unseen listener.”

“The detectaphone?” repeated Dillon.  “How does it work?”

“Well, for instance,” explained Garrick, “that attachment which I placed on the telephone is much more than a sensitive transmitter such as you are accustomed to use.  It is a form of that black disc which you saw me hide behind the pile of tires.  There are, in both, innumerable of the minutest globules of carbon which are floating around, as it were, making it alive at all times to every sound vibration and extremely sensitive even to the slightest sound waves.  In the case of the detectaphone transmitter, it only replaces the regular telephone transmitter and its presence will never be suspected.  It operates just as well when the receiver is hung up as when it is off the hook, as far as the purpose I have in mind is concerned, as you shall see soon.  I have put both forms in so that even if they find the one back of the tires, even the most suspicious person would not think that anything was contained in the telephone itself.  We are dealing with clever people and two anchors to windward are better than one.”

Dillon nodded approval, but by the look on his face it was evident that he did not understand the whole thing yet.

“That other disc, back of the tires,” went on Garrick, “is the ordinary detective form.  All that we need now is to find a place to install this receiving box—­all this stuff that is left over—­ the two batteries, the earpieces.  You see the whole thing is very compact.  I can get it down to six inches square and four inches thick, or I can have it arranged with earpieces so that at least six people can ‘listen in’ at once—­forms that can be used in detective work to meet all sorts of conditions.  Then there is another form of the thing, in a box about four inches square and, perhaps, nine or ten inches long which I may bring up later for another purpose when we find out what we are going to do with the ends of those wires that are now dangling on the outside of the window.  We must pick up the connection in some safe and inconspicuous place outside the garage.”

The window through which the wires passed seemed to open, as I had already noticed, on a little yard not much larger than a court.  Garrick opened the window and stuck his head out as far as the iron bars would permit.  He sniffed.  The odor was anything but pleasant.  It was a combination of “gas” from the garage and stale beer from the saloon.

“No doubt about it, that is a saloon,” remarked Garrick, “and they must pile empty kegs out there in the yard.  Let’s take a walk around the corner and see what the front of the place looks like.”