Hail A hail was a form of subspace communication between starship s , starbase s , and other ports of call . It was in use since at least the mid - 22nd century and could be digital ( computerized messages ) , audio , or visual . Most hails were visual , although routine operations could be handled by the computer or communications officer without requiring the commanding officer ' s involvement . In addition , hails could be audio - only . The treaty ending the Earth - Romulan War was negotiated entirely over audio channel s , as neither side had the technology to send visual images to the other . ( ) A hail , whether audio , visual , or computerized , involved two - way communications . A hail was sent by one party , and needed to be responded to by the other to initiate communications . When a recipient was unwilling to accept a hail , a one - way wide - band subspace transmission could be initiated by " opening a channel , " although it was customary to answer all hails . Such a message was usually not directed at any specific target , and there was no guarantee that it would not be intercepted even if it was earmarked for a specific recipient . In fact , there was no guarantee that it would be received at all . However , it could be reasonably assumed that any race that possessed the technology to receive these messages would probably view or listen to them out of curiosity , if nothing else . If needed , the receiving party could escalate the communication into a full two - way conversation by starting a return transmission . Frequencies . There were many subspace frequencies over which hails were sent . Most of the major power s , such as the United Federation of Planets and the Dominion , had their own frequencies and protocols for sending messages such as distress call s , but there were also general frequencies . ( ) When contacting a starship or space station the normal command was " open hailing frequencies " . ( ; , " et al . " ) Many types of atmospheric disturbance and certain element s or compounds would prevent hailing signals from reaching their destination . ( ) Engineer s could often find creative ways to solve this problem , but some conditions were impossible to penetrate . Jamming of hailing frequencies was a common technique used for purposes such as disrupting enemy communication in battle and preventing vessels from emitting a distress call . Most jamming techniques did not prevent the jamming party from sending out its own hails . Of particular note was the Breen method of sending out a rotating electromagnetic pulse . ( ) Types of hail . Non - contact hail . Hailing did not require direct communication with the other party ; messages relating to routine procedure or an unimportant matter could be handled via computer signals . For example , when Jem ' Hadar attack ship s requested ketracel - white from Dominion installations , the procedure was conducted entirely through computerized hails . It was more common for a computerized message to precede visual contact , however . ( ) When dealing with a vessel or location whose hailing protocols or capabilities were unknown , a general message could be sent over wide - band subspace . Additionally , wide - band subspace could be a technique for contacting anyone in the vicinity during dire situations . Standard hail . The most common type of hail was through audio or visual contact . The recipient had to first accept the transmission in order to initiate such contact . Making visual contact was normally standard , but it was not required . An audio link could be established when either a visual link was not possible or one did not wish to be seen . Some foreign entities were also incapable of a visual link and thus communicated over audio channels . The more common method involved a two - dimensional display showing the party on the other end . The area displaying the image was known as the viewscreen . One could pause the hail , which briefly stopped the transmission , as well as mute the other side when necessary . Standard hailing normally took place between two parties , although three - way hails were possible and were used on occasion . ( ; ) Holo - communications . Holo - communicator s were a new type of communications device used briefly by the United Federation of Planets circa 2373 . They utilized holographic technology to create a life - size version of the person on the other end of the hail . As Captain Benjamin Sisko said to Captain when he first used a holo - communicator , " " It looks like you ' re on my bridge ! " " ( ) Holo - filters . When making visual contact , a person could often use a holo - filter to mask their appearance . However , if the transmitting ship was scan ned at close range , sensor s could alert the recipients to the person ' s true identity . ( )