Cloaking device

In their war against the Federation, the Klingon Empire developed the a cloaking device, capable of rendering their warbirds undetectable to all sensors.

Fiction

Star Trek vs. Transformers

When the Decepticons made first contact with the Klingons, Kuri won over the skeptical Megatron by revealing the existence of the cloaking device. At Megatron's order, Trypticon scanned the downed Klingon ship, assimilating the cloaking device into his systems, putting it to good use by ambushing the the USS Enterprise. Prime's Directive, Part Two

Taking advantage of the Klingon dedication to victory at any cost, Starscream manipulated Kuri into giving him a cloaking device. Using it, Starscream slipped beneath the surface of Cygnus Seven as the battle raged and stole a bounty of dilithium. Unfortunately for him, he deactivated it too soon, allowing Megatron to see him flee the area. Prime's Directive, Part Four

Following Starscream, the Decepticons invaded the Klingon homeworld of Kronos only to be caught off-guard by a fleet of warbirds decloaking and overwhelming them. Prime's Directive, Part Five