Colored chalk pieces: Jupiter invented the concept of using these chalks to mark each of the detective's trails, and objects that they find. They mark using a question mark ("?"), which people might think was the mischievous work of naughty children. They also used different colors for each person, Jupiter used a white one, Pete used a blue one, and Bob used a green one, so that they would be able to know who marked the object or trail.
Ghost-to-Ghost Hookup: Jupiter invented this concept for "contacting thousands of boys without speaking to them directly". Each of the three boys contact five of their friends, apart from mutual friends, and inquire about something. If they know about it, they will answer, otherwise, they will contact five of their friends. This continues until the individual with the information contacts the sleuths, and receives the reward. Jupiter called it "ghost-to-ghost hookup" as only the inquirers' voices could be heard, making them somewhat like ghosts; also, it "had flavor and color".
Speaker phone: Because it would be difficult for all the three detectives to talk at the phone at once, when they were called, Jupiter created a microphone and speaker from parts of an old radio, that he kept close to the telephone, so that all three of them could hear what was said.
See-All: While the Headquarters had a great deal of secrecy and privacy, as it was covered by a pile of junk from the salvage yard artfully placed, its drawback was that it wasn't possible to know what happened outside the meeting place. As a remedy, Jupiter built a periscope, made out of "stovepipe with mirrors installed at angles in it", naming it, the "See-All". It rose through the roof close to the ventilation hatch. Anyone looking at it would only see an ordinary stovepipe.
Walkie-talkies: Jupiter had built three walkie-talkies for the three sleuths. All the three units could send and receive signals, but had a limited range of half a mile. The walkie-talkies, even though they had a very limited range, were very useful. It was because of the walkie-talkies that Jupiter and Pete's life was saved, as Bob was able to hear where they were taken through the walkie-talkies.