System interlock
A system interlock was a function of the transporter used to synchronize the pattern buffers of one or more transporter devices. The system interlock was essential to proper and safe transit between two connected transporter systems. 

In 2364, Natasha Yar attempted to interlock the 's transporter beam with that of the  to facilitate beam-out. ()

Engaging the interlock could cause ionic fluctuations to occur within the matter stream during transport. This was the case in 2369 when Reginald Barclay beamed back to the USS Enterprise-D from the  in the midst of a plasma streamer. Because of this, Barclay was able to see the quasi-energy microbes (actually members of Yosemites crew) that were trapped within the matter stream. ()

fr:Interlock système
Transporter technology