Sense spells vary on if they need to penetrate MR or not. The easiest way to tell is does the spell work by naturally occurring species (a natural sense) or magical ones (a magical sense). This is because if it can work on the naturally occurring species that things are releasing then the species are outside of the MR, but if it must create magical species they have to interact with the subject and thus its MR.
I broke it down in this thread, so it would be helpful if you read it and then ask any further questions you have to avoid duplication.