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I usually leave my iPhone(s aapl) plugged in to a power source right up until the moment I leave my apartment. But every once in a while I forget, and that’s usually the same day I don’t plan to come home for another 15 hours. Being without power for that long is painful, and I’m not the type of person to keep a spare Lightning cable on me at all times. But I’ve been carrying a Nomad ChargeKey with me for the last couple of weeks, and it essentially renders this problem obsolete.

Think about it: What’s the last thing you’re likely to leave the house without? I’ve forgotten my wallet once or twice, but unless you have a door that locks automatically, chances are your keys are just about guaranteed to go wherever you do. And that’s the beauty of the ChargeKey – it’s the same exact size as your average house key and it fits right on your key ring.

The idea is simple. One side of the ChargeKey is a Lightning connector that will fit into any Lightning port-equipped iOS device. The other side is a USB connector that can plug into a computer or USB power adapter. All you need is an available USB outlet to plug in to and you’re good to go.

The ChargeKey is capable of both charging and syncing your iDevice. It had no trouble working in any of the USB ports I tried, from a MacBook Air to an iPhone power adapter.

Since it’s the size of a key, the ChargeKey is pretty short. That makes it difficult to use with a desktop PC or a USB adapter plugged into the wall. It isn’t impossible – the device is made of a flexible rubber, so you can twist it around a bit. It just means your phone will be kind of dangling there (I wouldn’t recommend doing this with an iPad.) Plugged into a laptop, however, which is what I use to write with on a daily basis, the ChargeKey is a pretty perfect balance of form and function.

The only other misgiving I have is that both the USB and Lightning connectors on the ChargeKey are uncovered. I tend to throw my keys into a bag or a coat pocket filled with headphones and other small items, so it’s possible these connectors could get damaged. Since you aren’t likely to use the ChargeKey on a daily basis, it would’ve been nice to see some removable rubber caps around these connectors for protection.

Another thing I should note is that, while the ChargeKey works perfectly fine right now, Apple has been known to release software updates that disable unofficial Lightning cables in the past.

Finally, it’s worth noting that Nomad also makes a credit card-sharped Lightning charger (the ChargeCard) that fits in your wallet. I think this is another great solution for emergency charging on the go, and keeping the card in your wallet means the connection ports are less likely to get damaged. But like I said, I’ve left my wallet at home once or twice before.

For $25 (or a worthy barter), the complaints I have against the ChargeKey are sure to be forgotten the first time I’m really in a bind and need a quick charge for my phone. It’s just a few dollars more than a three-feet Lightning cable from Apple, and much more likely to be there for you when your battery’s at less than 10 percent.

The BlueLounge Kii is another solid option, and I like that its connectors are always covered, but it’s nearly twice the price of the ChargeKey. It’s also not flexible, so there’s a little less leeway with how you can use it. So for a quick emergency charge, Nomad’s ChargeKey is just about guaranteed to be there for you in an emergency. Unless you forgot your keys, that is, in which case you have bigger problems to take care of.