Shroud

The shroud was a built in ability to cloak found in the Jem'Hadar.

Shrouding made Jem'Hadar invisible to the naked eye and for the most part to sensors, showing up only as random pockets of collected energy. A shrouded Jem'Hadar had still to use it's cunning to stay quite so not to be detected and the bioelectric field they gave off could be detected by Andorian antennae.

In 2376 the Jem'Hadar Kitana'klan and Taran'atar beamed aboard Deep Space 9 and remained shrouded to hide their activity. Kitana'klan was revealed when the Andorian Shar detected him and threw a pitcher of fa'ntar at him which forced him to unshroud. (DS9 novel: Avatar)