Hmm. No, let's keep it to a calling to an object of Aetas - regardless of which one it is. I was thinking the travelers don't have much choice of their travel, the doors control it because the sister pieces are calling out to them. The Caligenians should be able to travel like they perform magic, quickly & easily. They've paid hefty prices, after all. I want them to feel like they have a free reign on the time scale, they can go wherever they want, whenever they want.
If they sense a piece of Aetas, it can just be a gut feeling or it could be something magical - like a fortune teller's ball lighting up, a rose dying out (using common examples, sorry! But if you could think of something unique that changes like alert, that works too).
let me know if you have more questions! Then I'll put this in the announcements as well!