Masking circuitry
Masking circuitry was a stealth technology observed by  in 2371 in use aboard a Kazon warship of the Kazon-Nistrim to minimize their sensor signature. 

The circuitry was not nearly as effective as a true cloaking device: ships employing them being somewhat detectable (as a "reflection") when they moved into certain angles from the sun. Ionization trails might also be detected. Furthermore, the effects of the circuitry could be temporarily defeated with a polaron burst.

Tuvok later speculated that the ship had been able to deceive the ship's sensors because someone aboard Voyager had sent instructions on how to perform such a deceit. ()
Shield technology