That's so cheap though, Mei <<; I mean, yeah, it works. But it's so damn cheap xD I have it so people need to find out IC first, to encourage some RP, but I didn't add that rule so someone could stand outside whatever village I am in, throw up their Byakugan or Sage Mode, and then BAM! That's lame as hell >>;
ANYWAY!!! Nah, I think if you found out through actual RP, whether it be the methods mentioned above, or even through a grapevine, no one can really just void you o.o
And seeing as you need to really know someone's chakra to use a Telescope technique, as you used in your example, then you REALLY would be able to find them xD... Of course, I don't see how that would even let you know that have a Bijuu >> There are no physical ways to tell and I don't think the telescope moves lets you feel chakra o.o Just see what's going on around said person, or what said person is doing.