Ruling on setting up a recorder to watch over a relative’s conversations
Question

                I have many brothers and sisters, so I use a telephone recording device to protect against wrongdoing and mischief. What do you think of this means, as this method has prevented wrongdoing in the past, noting that they are unaware of it?
Praise be to Allah.This question was put to Shaykh Muhammad ibn ‘Uthaymeen (may Allaah have mercy
on him) and he said:
I think that this is a kind of spying
and it is not permissible for anyone to spy on anyone else, because we have no
right the judge anybody except by what is apparent. If we start spying on
people we will have a lot of headaches because of this spying and we will be
upset by what we hear and see. 
Allaah says
(interpretation of the meaning) “And spy not” [al-Hujuraat
49:12]
after saying (interpretation of the meaning), “O you who believe! Avoid much
suspicion; indeed some suspicions are sins. And spy not” [al-Hujuraat 49:12].
But if the head of the household sees indications
of these evil telephone calls, then there is nothing wrong with setting up a
recording device without their knowledge, but he realizes that there is
something going on, he should not keep quiet and keep listening, rather he
should rebuke them straightaway, because if he communities to listen,because he may hear
something that will upset him even more. For example, if he comes across a bad
telephone conversation, he must rebuke the one who is doing it straight away,
and not delay it until the next day; he must put a stop to it from the
beginning.
But with regard to mere suspicion
based on waswaas (insinuating whispers of the Shaytaan), it is not permitted (for him to set up this
device), but if he knows that the matter is serious and that it is actually
happening, then it is OK to set up a recorder so as to find out what is going on.