REASONS TO BUY
Effectively prevents cross-loading
Reasonably affordable
Relatively light
REASONS TO AVOID
Very small gate openings
Opening top gate causes other to automatically open
Not super versatile
Mad Rock Gemini Review
A belay locker that is effective and relatively affordable, but feels gimmicky
Credit: Backcountry
RELATED: Best Locking Carabiner of 2024
Our Verdict
The Mad Rock Gemini is a locking carabiner designed specifically for belaying that actually has two gates. Not only that, but it also has two separate chambers and openings, joined in the middle, making it one of the most unique, and bizarre, locking carabiner designs that we have tested. The purpose behind this design is to prevent the locker, or belay device, from rotating when belaying, and thereby avoiding cross-loading. It does this well, but at times comes across as perhaps a bit too complicated to achieve this purpose. While there is only one screw down lock, the hinges of the two gates overlap so if one gate is locked, the other one is also pinned closed. The two gates can also open at the same time, but the very small gate openings limit it to belay use. While it may look weird, the Gemini is an affordable and effective belay locker, but doesn't have much use for any other purpose.
Compare to Similar Products
 This Product
Mad Rock Gemini | |||||
|---|---|---|---|---|---|
| Awards |  Best Overall Locking Carabiner |  Best Offset-D Shaped Locker |  Best Bang for the Buck | Best Compact Locker | |
| Price | $13.00 at Backcountry Compare at 2 sellers | $18.95 at REI Compare at 4 sellers | $22.95 at REI Compare at 3 sellers | $9.69 at REI Compare at 3 sellers | $14.95 at Backcountry Compare at 4 sellers |
Overall Score  |
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| Star Rating | |||||
| Bottom Line | An anti-crossloading locker with two gate openings that hinge on each other in a rather complicated design | The longtime standard as the best locker for all purposes | A lightweight, simple, twist-locking offset-D that performs better than the rest | Our Best Bang for the Buck winner due to its great price, but also its impressively lightweight | The lightest and easiest to use small locker |
| Rating Categories | Mad Rock Gemini | Petzl Attache | Petzl Sm'D Twist-Lock | CAMP USA Photon Lock | DMM Phantom |
| Overall Utility (25%) | |||||
| Ease of Unlocking and Locking (25%) | |||||
| Compactness and Weight (20%) | |||||
| Gate Security (20%) | |||||
| Gate Clearance (10%) | |||||
| Specs | Mad Rock Gemini | Petzl Attache | Petzl Sm'D Twist-Lock | CAMP USA Photon Lock | DMM Phantom |
| Weight | 72 g | 57 g | 51 g | 44 g | 41 g |
| Gate Closed Strength (KN) | 23 | 22 | 23 | 23 | 24 |
| Sideways Strength (KN) | 7 | 7 | 8 | 8 | 9 |
| Gate Open Strength (KN) | 7 | 6 | 7 | 9 | 9 |
| Gate Clearance (cm) | 1.6 cm | 2.6 cm | 2.2 cm | 1.8 cm | 1.6 cm |
| Visual Locking Indicator? | Yes | Yes | Autolocking | Yes | No |
| Carabiner Shape | Dual Opening | Pear/HMS | Offset-D | Offset-D | Offset-D |
| Lock Closure Type | Screw Lock | Screw-lock | Twistlock, also comes in screw lock or triple action | Screwgate | Screwgate |
Show full specification details ▼Hide full specification details ▲
Our Analysis and Test Results
The Mad Rock Gemini is designed to prevent cross-loading while belaying, and for this purpose we found it to be quite effective. It has two gates that are linked together at the hinges, meaning that both gates are locked with a single screw-lock device. One gate is meant to be attached to the belay loop, and the other is meant to be attached to the belay device. Unfortunately, these overlapping hinges also mean that if you want to open the belay loop gate, the belay device gate opens automatically. This is not awesome if you are taking the locker off of a gear loop on your harness, as it is easy to accidentally drop the belay device off the lower nose, which is shallow. Because it is pretty much two tiny carabiners fused into one, the same problems we have with small carabiners also manifest — namely that they are harder to manipulate due to small gate openings. Despite our complaints we found this carabiner relatively easy to use, although if you want a versatile option that can work for multiple purposes, you should look elsewhere.
Performance Comparison
Rappelling is one of the situations where it can be nice to have an anti-cross-loading carabiner, although after weighting the rappel, there is very little to no chance for a shift to take place that would crossload, so it isn't really necessary. While we tested the Gemini in the Bugaboos, its small basket with thin stock wasn't our favorite for rapelling with two ropes, as we are here on the Kain route of Bugaboo Spire.
Overall Utility
We found this carabiner generally does not perform as well as simpler, more standard pear or HMS shaped lockers, which we prefer for their ease of use as well as simplicity. While this locker works fine for use with a GriGri or other active assisted braking device, the small openings and upper basket make it a bit harder to use with an ATC, and not exactly ideal for rappelling with two ropes. The fact that both gates must open together means there is a greater risk of dropping a belay device off the top basket when removing the lower gate from your belay loop or a gear loop. Additionally, since the lower gate is pinned by the upper gate, to open it requires overcoming dual spring loaded gates, which is harder than simply opening a single gate, and oddly enough led to the gate closing with such force that more than once it pinched our skin. The small gate openings and small baskets mean it isn't super versatile for building anchors. While it isn't as hard to use as we are making it sound, it also isn't as simple as a regular old locker.
The Gemini is a very unique locker with two chambers and two gates, it is almost like two carabiners attached into one. This design separates the belay loop from the belay device to prevent cross-loading situations, and is quite effective. As you can see here, the lower, red gate has hinges that are pinned by the upper, locking gate, so if the upper gate is locked, so is the bottom one.
When the top gate is unlocked and you open the bottom gate, both gates are automatically opened. Functionally, this doesn't help performance or use at all, but is a side effect of having the pinned hinges so there can be only one locking mechanism. Due to the small gate clearance and small baskets, we found this locker to not be super effective for uses other than belaying.
Ease of Unlocking and Locking
Since the two gates are pinned at the hinge, if you lock the top gate, then both gates will automatically be locked. There is no way to lock the lower gate by itself. To lock the gates a simple screw lock mechanism is involved. This screw locking mechanism is small, and only has added texture at the top and bottom, with slippery un-textured metal in the middle, making it not the absolute easiest to grip compared to the competition. We measured seven half rotations, or 3.5 full rotations, to go from fully locked to fully unlocked, which is also not the least that we tested.
To lock both gates of this carabiner simply tighten the screw lock mechanism. In all circumstances, both gates are either locked, or both are unlocked. You can see the visual indicator stripe, which is red, under the screw lock mechanism on the top gate. If you can see this stripe it means the gate isn't fully locked, and if this stripe is covered it means that it is locked.
Compactness and Weight
We measured the weight of the Gemini to be 72g on our independent scale, which actually makes it one of the lighter belay specific carabiners you can buy, but not by any means as light as a standard HMS or pear shaped locker. However, we bumped its score for this metric down a tad because of how large it is. It is taller than all of the others that we tested, so we can't consider it to be especially compact.
At 72g, this locker is among the lightest belay specific 'biners you can buy, but nowhere near as light as a standard HMS style locker, or the most lightweight and compact choices.
Gate Security
The Gemini features a single screw gate to lock it, which we find to be among the least secure. This isn't to suggest that they cannot be trusted, simply that screw gates have the notable flaw of needing to be remembered to be locked, rather than simply locking themselves. The screw gate on this locker has a red stripe that wraps around the gate to serve as a visual indicator: when it is fully locked, the stripe will not be visible. If you see red, then it isn't locked.
One of the things to be aware of when using this locker is the fact that when you open the non-locker side, the other gate also opens automatically. With a small, shallow nose, this means that simply removing the 'biner from your harness could easily lead to spilling your belay device off the climb, which would be a bummer.
We can't decide whether having two gates makes it less secure or not. If you forget to lock it, then there are two potential gates that could conceivably open, instead of just one, but we can't really imagine scenarios where this might happen.
Gate Clearance
We measured the gate clearance for this locker at 1.6cm, which is among the lowest scores for this category. Both the top and bottom gates open the same distance, although if you open the bottom gate as far as you can, it automatically opens the top gate to a distance of only 1.2cm, which is the “gate clearance” number listed on Mad Rock's website. From a functional standpoint, larger openings greatly ease general use, and the very small openings on both ends of this carabiner are certainly a draw back, making us less likely to want to use it for anything besides belaying.
We measured the gate clearance for both sides of this locker (bottom side shown) at 16mm, ranking it among the smallest lockers in this review, and somewhat limiting its functionality.
Comparing the amount of gate clearance between the Gemini on the left, and the DMM Rhino on the right. You can see that the Rhino has far more clearance, and also a much larger basket for holding knots. It is far more functional for uses other than belaying due to this design shape.
Value
The Gemini is nowhere near as expensive as some of the higher priced belay-specific carabiners, but still costs slightly more our favorite belay specific carabiner, or even our favorite HMS shaped one. While the price isn't out of line with performance, we would prefer to spend the same amount of money on a better product.
Testing the Gemini in a somewhat cluttered anchor (sorry) on a multi-pitch climb to see how it works for non-standard belaying. We have it attached to the equalized sling, holding the Petzl Reverso as we belay up the second. While it worked out alright in this situation, the small, dual gates, made it less easy to manipulate in this crowded anchor.
Conclusion
The Mad Rock Gemini is one of the most unique locking carabiners we have ever used, with two separate “chambers” accessed by two different gates, which both manage to lock with one single screw lock mechanism. While it works decently for belaying, it isn't super versatile for other applications. While we don't think it's a bad product, we would sooner recommend others for the purpose of preventing cross-loading.
Descending the Bugaboo-Snowpatch Col in the Bugaboos in late summer means rappelling through loose, steep dirt and boulders, made worse by having to do it in a rain storm. Multiple rappels like we did here pointed out one of the main flaws with the Gemini -- the ease with which one could accidentally drop their belay device because both gates must open at once. We narrowly avoided doing so twice, and then simply shifted lockers to make sure it didn't happen.
—
Andy Wellman
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