I haven't tested this myself, but I rarely warrant an immortal to actually actively 'follow' me as it were.
But I imagine if you cast "receiving voice" that if an immortal were to enter the room, it might likely trigger it.

Just a thought on how it may work (even if they are wizinvis)
So, I leave the title obscure, so you can dictate whether it is bugged/tobefixed, or not relevant at all.

Thanks.