Is there a word for 'calling out to anyone who may respond'?

Solution 1:

There are phrases (and related verbs and nouns) that describe the first two such as give a holler

This is related to the verb holler

to shout or yell (something)

but it has a less excited quality, and is often used to refer to a greeting, and can even be used to convey contact me.

A similar term is give a shout. This also has a less urgent tone than the verb shout

These terms could be used to refer to electronic communication, but this usage is probably not very common. It has a bit of an oxymoronic quality (electronic amplification eliminates the need to holler or shout).

A related phrase specifically used on broadcast media is give a shout-out

a greeting, especially when someone on the radio sends the greeting to someone who might be listening

Another term commonly used for the electronic shout on a computer line to see if someone is there is ping

to send a test message to (a computer or server) in order to check whether it is responding or how long it takes it to respond

Solution 2:

the word that I can immediately think of is

halloo

a shout to attract attention, esp to call hounds at a hunt

Used to catch someone's attention.

To call out to.

(source: freedictionary.com)

Solution 3:

You can use

challenge: transitive verb 2: to order to halt and prove identity the sentry challenged the stranger

or

challenge: noun 2a : a calling to account or into question c : a sentry's command to halt and prove identity

from m-w.com