they don't however, need to provide a warrant for their own apartment. that's effectively what slack is implementing, it does not mean that they can go through your personal slack setups. just fyi, any application that is provided by your employer is theirs and most likely in your contract is that everything you say or write is their own property.

if your mobile is paid for by your employer, they have access to anything on that as well, this include texts, mms, and call logs.