Although he has many powers, Peter Parker's greatest strength just might be his intelligence. With his scientific prowess, Spider-Man has invented a number of devices to help him be a hero. Although Spider-Man's web-shooters are his most well-known gadgets, his most useful invention might just be the Spider-Tracer.
Peter's underrated invention first appeared in 1964's Amazing Spider-Man #11, by Stan Lee and Steve Ditko. The Spider-Tracers were small, spider-shaped trackers that Spider-Man invented to pursue his enemies when he couldn't do so himself. When Doctor Octopus was released from prison, Peter developed the Spider-Tracer to track Octavius to his new hideout without being seen.
Over time, Peter developed his Spider-Tracers so they could shoot out of his web-shooters, indicating how often he used them. Generally, the Spider-Tracers haven't received as much attention as the web-shooters, even though they're just as impressive, if not more so. Just like his web-shooters, Peter invented the Spider-Tracers while he was still in high school.
Any time that Spider-Man was losing a fight or one of his enemies was getting away, he could simply throw a Spider-Tracer at his opponent, biding his time until later. In a way, this is more useful than Spider-Man's web-shooters, enabling Peter to rest or gain time to prepare against an enemy. Moreover, the Spider-Tracers were introduced in the 1960s, decades before tracking technology of this caliber was developed in the real world.
Nowadays, tracking technology like the Spider-Tracer plays an important role in many areas of life. It's incredibly impressive that a high school student, in the '60s, no less, would invent technology that would become more relevant as time went on. Initially, the Spider-Tracers were connected to an electronic receiver which tracked their location.
This aspect of the Spider-Tracers was impressive enough. Yet, as Peter developed his Spider-Tracers, he adjusted them to emit a signal that his Spider-Sense could follow. It's incredibly innovative that Peter could adjust his Spider-Tracers in such a way, making them accessible by using nothing but his Spider-Sense.
This new innovation made it hard for enemies to intercept the Spider-Tracer's signal, unless they had Spider-Sense as well. Spider-Tracers don't just track Spider-Man's foes, either. For a time, Mary Jane wore a Spider-Tracer as a necklace. This way, if MJ was ever in trouble, Peter could find her easily.
It's true that web-shooters are also impressive, considering their variety of applications during Spider-Man's adventures. Spider-Man's webs can be used for swinging, creating safety nets or any number of creative applications. Peter also invented these web-shooters as a high schooler, which is an astounding achievement.
Even so, Peter's web-shooters haven't quite found their market for a wider audience. Spider-Tracers, on the other hand, were developed for broader applications in 2015's Amazing Spider-Man #2, by Dan Slott and Giuseppe Camuncoli. When Peter was the head of Parker Industries, he sold his Spider-Tracer technology as a means to track his Webware devices.
If anyone lost their Webware, they could use the tracking technology of the Spider-Tracer to find their device. Peter has tried to sell his web fluid for similar purposes, but people have rarely bought into the practicality of web fluid for a broader application. Spider-Tracers, on the other hand, could be used to track people or technology, for commercial or military applications.
It makes sense that Spider-Tracers are overlooked. Web-shooters are used much more overtly, coming into play any time that Spider-Man goes web-swinging. Yet Spider-Tracers have a much broader application, taken for granted due to their less visual nature. Not only can Spider-Man use his Spider-Tracers for a variety of purposes, he can also mass-produce these devices for the world at large.