1a.) To my knowledge, Naruto is the first Kyuubi Jinchuuriki to gain control over the Kyuubi, granted he doesn't have friendly terms with the Kyuubi yet, but it is something Kishi is foreshadowing and beyond the scope of this thread.
1b.) Once he took the Kyuubi's chakra and whenever he uses it, he can sense hostility. As noted by the Kisame, this an ability beyond any other sensor ninja and must've come with gaining gaining control of the Kyuubi's chakra.
2.) However on the very first panel of 545 we learn from Madara that Mito Uzumaki also had this ability. Hence, his trap with the white Zetsus to lure Naruto out.
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She sealed the entire Kyuubi in herself during the fight between Hashirama and Madara at the Valley of the End. However, how does she have this ability if she and Kushina were never more than containers for Kyuubi rather than in command? Is this some sort of Uzumaki Kyuubi chakra synergism?
3.) Kushina had an eight-trigrams seal specially made for her by Minato and with her assistance. Then I wonder if it has something to do with the seal. For example, did Kushina and Mito use different seals, and Naruto's new seal is closer to Mito's?
To summarize, we know Naruto gained the ability to sense hostility only after gaining control of the Kyuubi's chakra for himself. To our knowledge, he's the first to do so, and Mito and Kushina merely acted as vessels for the Bijou.
Thus, how did Mito gain the ability to sense hostility, given she was a vessel and not in control like Naruto is. Perhaps, it was there all along. Perhaps it has something to do with Uzumaki - Kyuubi chakra synergy (which we know Kushina at least had), perhaps it has to do with the seal used by Naruto currently and Mito.
The one factor that's obvious, but significant is the Uzumaki lineage that they share. However, there must be more because Kushina has not been stated to have this ability, perhaps her special chakra suppressed it.
As you can see there is very little information to go on, so feel free to speculate here. I'm not one to condemn it as long as it's reasonable and based on good intentions.
We'll probably get the answer when the trap is sprung on Naruto by Madara, albeit I have a feeling Bee will sacrifice himself at that point given the track record of Naruto's teachers.
I don't know the answer though I'd like to, and I'd like to hear your opinions, so feel free to post, or just glance, whichever suits you.
Peace