I like the explosion thing, but I think it should be an explosion that does NOT do damage. It explodes and debuffs all enemy player's stealth detection within it's radius and makes all enemies in the blast radius unable to stealth/turn invisible for 30 seconds or something. That would be great. It still detects stealth, so you could watch through it and set it off whenever a stealthed enemy is near. It could be activated by you at any time of your choosing, or at the end of 5 minutes, whichever comes first.

As for a current use, it works well for calling out incomings to the Gold Mine in AB. Sure, you can use farsight, but you have to cast it everytime you use it. With the sentry totem, I can, as Ron Popeil would say, set it and forget it. I can run around get in position, check at the top of the Gold mine ramp with my sentry totem, then go back to my view, attack an enemy, kill him, and check again for more people coming with my sentry totem. I don't have to REcast it each time unless it's been 5 minutes. So, it would probably be less mana. Also, if I happen to NOT be looking at it at the time, and someone kills it, I still know they are coming.

Anyway, it is completely useless other than that and I agree that it should get some kind of buff.