They definitely get warrants to plant listening devices. LE suspected Christopher Hill and Lukas Kamay for months of insider trading but they couldn't nail them because the 2 were using burner phones. The lucky break came from a LD inside one of their cars and the 2 had a full on conversation about their entire insider trading scheme, biggest in Aus history at the time.RSBM
I've never heard of LE installing LDs in someone's house to check their mental state. They'd have to get a warrant and to do that they'd have to provide a judge with very good reasons for wanting them as LDs are an extreme invasion of privacy. If they had reason to believe he might murder his family, harm the public or commit suicide, they might be good reasons, but where would they get that information from?
LE could have made enquiries at Jetstar.
"Jetstar has been advised by Victoria Police that one of its employees is under investigation for a serious crime and will work to assist in this due process any way we can. As a matter of course, the employee has been removed from duty as a result of their arrest."
Jetstar confirms it is standing down a pilot as police question the man over missing campers
Highly recommend the podcast The Sure Thing about this case
'It was just chaos': The day police cracked an $8 million scam