dbus-ping

dbus-ping is a compiled Lisp function in `dbus.el'.

(dbus-ping BUS SERVICE &optional TIMEOUT)

Check whether SERVICE is registered for D-Bus BUS.
TIMEOUT, a nonnegative integer, specifies the maximum number of
milliseconds `dbus-ping' must return. The default value is 25,000.

Note, that this autoloads SERVICE if it is not running yet. If
it shall be checked whether SERVICE is already running, one shall
apply

(member service (dbus-list-known-names bus))