Tricorder

A tricorder is a portable sensing and computing device used by many civilizations in Star Trek. Designs vary by producing organization and application, but all tricorders seem to be able to perform active scans and evaluate the results using an internal database.

Limitations

Tricorders seem to use active scans exclusively, so they are likely to give away the location of the user to anyone with the means to detect their signals.

Tricorders are unreliable at detecting unfamiliar phenomena. For example, they are unlikely to detect devices based on technologies that are not known to the Federation.

Tricorders rely heavily on electromagnetic recognition. Masking a person's electromagic field, for example, can hide that person from tricorder scans.