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Polymath Products CMP-20 Compass Necklace Review – Lightweight, Accurate, and Built to Survive
- UKSN
- 5 hours ago
- 4 min read
The CMP-20 Compass Necklace from Polymath Products is a stripped-back, rugged navigation tool designed for fast access and reliable performance in the field. While it shares the same core compass as the NV-20K (which we recently reviewed), it ditches the rear photoluminescent map-reading lamp in favour of a longer neck cord, making it ideal for users who want simple, immediate direction-checking capability on the go.
Whether you're hiking, biking, paddling, or just keeping it as part of your EDC, the CMP-20 offers a no-nonsense, military-grade build in an incredibly compact and wearable form. If you're someone who doesn’t need the rear illumination feature, this might be the smarter choice.
Polymath Products CMP-20 Pros & Cons
Pros:
Very accurate for its size
Military-grade durability and shockproof design
Oil and seawater resistant
Can be worn around the neck for easy access
Glow-in-the-dark dial is easy to read at night
Lightweight and unobtrusive
Great value for money
Made in the UK
Cons:
No rear photoluminescent map lamp (available on NV-20 model)
Needs to be held flat and away from electronics to remain accurate
Lacks direction-of-travel markings for more complex navigation
No safety breakaway in case it becomes snagged
UKSN Rating: ★★ (2/4)
Durability & Construction
Just like its sibling, the CMP-20 is built to survive extreme conditions. It uses an oil-bath sealed compass capsule within a shockproof, flexible TPU shell. The result? A tool that’s nearly indestructible under typical field use.
Rated for temperatures from -30°C to +50°C and pressure-tested to depths of up to 80m, this thing is as comfortable being submerged as it is riding on your chest during a storm. The materials are non-metallic and non-magnetic, so the compass stays true and with zero flex in the housing, it feels solid and trustworthy in-hand. One thing to note: the included cord does not feature a safety breakaway. For something worn around the neck, this would’ve been a welcome addition, particularly for those using it in more rugged or overgrown environments. We highly recommend adding a breakaway link if you plan to wear it regularly, both for comfort and safety.
Size, Weight & Cord
At just 11.6g and 35mm x 27mm in size, the CMP-20 is barely noticeable when worn. The cord is a full 800mm in total length (400mm loop), which is long enough to wear comfortably around your neck over or under layers. This makes it perfect for hands-free use, allowing you to make quick directional checks without rummaging through gear or pockets.
It’s a smart alternative to zip-pull style compasses if you want something always available -but not dangling in the way.
Low-Light Performance
The CMP-20 features a photoluminescent dial that glows after being exposed to a light source — ideal for night use. It’s bright enough for quick glances and stays readable without being overpowering or compromising your night vision.
That said, if you also want to read maps or have a personal marker light, you’ll want to step up to the NV-20 Compass Necklace, which includes the rear-facing glow lamp. Personally, that’s the one I’d go for — I find the additional illumination handy, especially when navigating in darkness. But if you know you’ll never need that extra light, the CMP-20 keeps things sleek and simple.
Accuracy & Use in the Field
One thing that many of you likely already know, but it’s always worth a reminder is that these types of compasses must be held flat for best accuracy. During testing, we found that if it’s placed near tech (like a phone, watch, or GPS), it can easily be thrown off. A gentle shake while keeping it flat helps the needle re-centre smoothly and quickly.
Out in the field, though, where it’s free from interference, it performs reliably and consistently - a major plus for something this small. Compared to typical “button compasses,” this is in a league of its own.
CMP-20 Compass Necklace Final Thoughts
The Polymath Products CMP-20 Compass Necklace is a simple, tough, and brilliantly wearable navigation backup. It does what it’s meant to do, and it does it well. With military-grade materials, high accuracy, and a dial that’s visible even in the dark, it’s ideal for anyone who wants a no-fuss compass that’s always ready.
If you value lightweight simplicity and don’t need the rear lamp, this is the version to go for. If however you want that bit of extra low-light functionality, spend the few quid more and get the NV-20 Compass Necklace instead, you won’t regret it.
One thing we’d love to see in future versions is a safety breakaway on the neck cord. While it’s easy enough to add your own, it would be a smart inclusion from the get-go, especially for users heading into thick brush or dynamic environments.
Either way, Polymath Products has delivered another outstanding bit of kit that punches well above its size.
Save 10% on Your Polymath Products Order!
Thinking of picking one up? You can save 10% on any order directly from Polymath Products by using our exclusive code: UKSN
Whether you're upgrading your kit or buying your first mini compass, a little discount goes a long way. Plus, you can feel good about supporting a small independent British company!
🎁 Win a CMP-20 Compass Necklace!
Want to get your hands on a Polymath Products CMP-20 Compass Necklace for free?
We regularly give away gear in the UKSN community, and this could be your chance! To enter:
👉 Join our WhatsApp Competition Channel and take part in our latest giveaway which goes live later today (16/6/25). FYI the competition can be found in the channels description.
It’s quick, easy, and open to all UKSN members (free & paid). Don’t miss out, you could be testing one of these yourself on your next adventure.
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