From the Wikia
Spider-Man uses a small electronic receiver to follow the signals of his tracers, ...
but eventually he modifies the tracers to emit a signal he can follow with his spider-sense so that he will be able to know whether or not he is in the proximity of the tracer
Also from the Wikia
A teen Spider-Man invented his first Spider-Tracer to find Doctor Octopus. In those early times he invented a receiver device as well. Spider-Man eventually found out that changing the frequency emitted by the Tracers he could trace them with his Spider-sense.
As for others using the tracers
Besides Spider-Man, Daredevil can pick up the signal with his Radar Sense from the Spider-Tracers due to his heightened sense of hearing being able to hear the signal. Unlike Spider-Man, it is more difficult for Daredevil to follow the signal, as he must drown out all other sounds around him to maintain focus.
Using his resources at Parker Industries, Peter Parker built an improved version of the Spider-Tracer. He made it available for commercial use, having the option of being linked to a webware. The new spider-tracer featured a two-year battery life, was water-proof, and was super durable.