The rift detector is available to people who caught the moussile mouse at the birthday event. Otherwise, it'll be available through the Living Garden Cartographer.

Details from the news story

Looks like you will need access to the Living Garden for the new area. The cheese is pricey.

Edit: One recipe has already been discovered. Magical String Cheese:

Based on my brief foray into the Rift and my research on the MH fora, I'm going to finish my M400 assignment and try to focus on the LG to get my Rift Base. I don't think the Rift Base will add much until I get the trap, but I feel like I want to have that bought before I start buying such expensive cheese on a regular basis. The Brie String is only cheaper than Lunaria as far as LG cheese go, though the mice in the Rift seem to be pretty good for gold when you catch them.

All the high level areas seem to be grinding/farming areas where you need to go through a lot of each level to complete the area, which is nice on the one hand, but not so much when I still haven't finished any of the areas and they keep adding more.

First impressions from this morning and early afternoon of the new Rift area...
Positives: The Artwork. Don't I always say that? But I really mean it this time. I love it.
The Concept. The "upgraded" Meadow mice are cracking me up. There's a few mice that I'll need to catch to figure out which mouse they're supposed to be, but the ones I have so far are hilarious. I bet the Brawny Mouse was fun to draw because whoever did it had to go back to the basic line drawing of the White Mouse.
The Difficulty. I already know there will be many disagreements on this, but I love the fact that this area is properly hard. It's bringing me back to my Derr Dunes days when I arrived with nothing but a Digby Drillbot and the Explosive Base and I had two catches per journal page. Actually, I'm doing better than that, but only because I'm attracting the "little" mice.

Negatives: Lack of strategy (so far anyways). This is kind of a selfish one because I know that most people can't handle Z's Tower and Warpath locations because they're busy. But I prefer an area that's more interactive rather than arm the cheese and hit the horn. *cough*boring*cough* Maybe it's too early on and this will change later, but that's my first impression.
Lack of pals. Due to both the slow nature of the area and the fact that this is what I consider to be the current final stage of the game, I don't think I'm going to have a lot of hunting buddies here, which is kind of a bummer.
Resource hog. Mixed feelings on this one, but as far as I can tell, we're going to be losing gold hunting here. That's ok though, when there's either a Toxic Spill or a train to help out with, I won't have any qualms about taking a break for a bit.
No Ronza. 'Nuff said.

Personal progress so far. I've caught 4/16 types of mice, but have not gotten a single potion.

My strongest trap is the Sphynx Wrath, and she really isn't strong enough for the Rift area. I went in and hunted for a few hours just to have a taste of it - and I might come back occasionally to try to fill up some more silhouettes - but I don't think I'll be able to do any serious hunting there until I've opened the Living Garden and got the upgraded traps from there. And then we're talking months ...

I agree about the Artwork - I really like those mice!

I'll go get some more gold (from Mojos) first of all, though ...

I guess I'm having great luck then.

I've caught 15 mice total, with 8/16 breeds nabbed

I got a total of 4 potion drops out of about 10 mice. I used the super stringy cheese for transformations, so that gave me 20 pieces of Riftiago cheese. I've been using ultimate charms to help me, and have nabbed two new mice since then.

We'll see what happens next

12 mice caught so far. 8 out of the 16 breeds. 2 potion drops.

I'm using the Sphynx Wrath + Rift base + Brie string cheese + ancient charms.

I started out with my monstrobot and marble string cheese and switched out with the kitty when I didn't catch anything. I did hunt with the Magical String Cheese for five hunts, but I'm being cautious until someone has the time to figure out if this is a break even area or a major gold drain without the rift trap. I don't want to lose too much before Ronza comes.

I actually like the area and I do think there's strategy to come. It's also nice to have something that involves the Living Garden as a jump off point.

Well, I'm convinced that the Market Guards are conspiring to keep me from finishing this M400 assignment. Every time I attract one with my best setup, I miss it. The Market Thieves, however, I catch every time, despite their being the same difficulty according to my effectiveness meter.

I'm thinking that this area is going to turn out to be a bigger, badder version of Balack's Cove. Here's why I think that:

Just my thoughts. . . but at any rate, I can't see them being "finished" with this area. To me it seems that if you got lucky, you could finish it in a week or so if you really wanted to.

DiGs, I think you're right on with your conclusion. I think there will be some people who get really lucky, just like they did with Balack, and finish this area up immediately. And I'm sure I won't be one of those people.
But on the other hand, they seem to be in mini-area mode. Lots of small but difficult areas that they can push out quickly to give us something to do and open up storylines for future releases. Considering that they have yet another new area coming once Easter is over, it wouldn't surprise me if this is all there is to the Rift; for now anyway.

As of this morning, I've had multiple potion drops, caught 10/16 mice, attracted 13/16, and have two dust, one seed, and one grass. The mouse I'm cracking up that I haven't caught yet is the Supernatural mouse because EVERYBODY else has several of those.
I was wondering if anyone has attracted the Wealth mouse? Haven't seen him yet.

I haven't had any of the drops beyond the potions yet. Wonder if I should switch to luck charms instead of ancient.

Any tips?

The drops you only get from the mice that are attracted with Riftiago cheese.

Ok. Thanks fantasia. I'll try swapping out for some of my luck charms and the cheese. I wasn't sure if I'd have any luck with that cheese until getting the trap, but I doubt I'll get the trap without it.

I attracted a wealth mouse, FK.

I've been having lots of good luck this morning... yay! I got enough ingredients to craft my first Resonator Cheese, which I did. But there was a big warning sign which said "This is going to be tough until I find a Rift-type trap." I went on one hunt which was an FTC of the Goliath Field and then figured I'd better save the rest of the cheese until I know for sure that crystal drops off of him. On the off-chance it's crafted with other ingredients, I don't want to waste my hard-earned cheese. So I'm back to regular Brie String cheese in the hopes of catching the Supernatural and Dream Drifter. I just need those two and the Wealth (and obviously Goliath) and then I've caught all the mice.

Thanks for the note on the Wealth Mouse DiGs!

Well, griping in here seems to have done the trick. I caught the Market Guard, a Bionic in the Meadow, and my fourth M400.

I'm now settling into the Rift area for a bit. I've only caught 3 breeds of mice so far and looted 1 Riftiago potion. I went ahead and crafted Magical String Cheese to convert with the potion so as to get the most bang for my String Brie buck. I'll stick to this area for a bit and then try for more progress on M400/LG stuff.