LISTENING DEVICES ACT 2009 A.C.T

(3) Subsection (1) (b) does not apply to the use of a listening device by,
or on behalf of, a party to a private conversation if—
(a) each principal party to the conversation consents to that use of
the listening device; or
(b) a principal party to the conversation consents to the listening
device being so used, and—
(i) the recording of the conversation is considered by that
principal party, on reasonable grounds, to be necessary
for the protection of that principal party’s lawful interests;

From memory, this is identical to the Commonwealth legislation