The goal is to find a lock solution for urban bike-commuting kids. Something that is safe enough to leave all day, light enough to not mind carrying on the bike or in a backpack, and easy to use. Ideally, something kids will want to use, and can use on their own.
Our first stop was Pinhead. They recently released the City Lock Ultimate Pack, which includes a lock, Pinhead wheel locks, Pinhead 
Seatpost Lock, Pinhead Headset Lock, and two keys. It also includes a carrying bracket for the lock with is designed to attach to a frame’s main triangle. The lock is advertised as being 660g, which is pretty light for a high-security lock.
Pinhead began with a simple bike security idea. The created something that could replace quick-release skewers with a secure solution. The product is a narrow, threaded rod with a low-profile convex disc on one end and a round convex nut with a unique pinholed arrangement on the other. A matching concave disc with pins sticking out of it and a lever on the end is how these wheel releases are tightened and loosened. This simple system makes it hard for wheels to be stolen off a bike, while still providing easy removal, so long as you have the matching keyed lever on your key ring or in your bag.
The product has been a success. It’s light and small and can easily be retrofitted into pretty much every hollow-axle hub. And when Pinhead found out that a certain tool could defeat it, they created a fix, Pog washers, to prevent that. They even have axle-nut and thru-axle versions. If there’s a limitation, it’s with the need to bring along the tool whenever you ride the Pinhead-equipped bike. Yes, it’s only a few grams (actually 33), but it takes up space, adds weight, you have to remember to carry it along, and not everyone likes having something so bulky on their key ring, especially if they’re already carrying a key for their bike lock. But, because the pin designs are numbered with a nine-digit key code etched into the lever, the user can not only order replacement keys, but also extra skewer nuts, so that the one key can be used on multiple bikes, like your entire fleet, or family’s fleet. Or you can have many keys in many bags and key rings, so you’re covered no matter what.
Pinhead has expanded their offerings by making a suite of bike security products that all work off the same pinned key. They’ve made a bolt for the preload on Aheadset-style stems, a seatpost clamp, a clamp to prevent saddle theft, and, most importantly, their own lock. When they all work off the same key, it simplifies the process of locking up and lightens the load.
Their lock is smallish and rigid and a good bit lighter than the competition. The shackle measures 13mm thick by 35mm wide, has an interior dimension of 83mm by 181mm. Our sample weighed in at 628g (1lb, 6oz). It’s hinged for opening and closing and covered in what appears to be a durable nylon fabric. The locking mechanism is shrouded by the aluminum lock body, making it difficult for thieves to attack the lock mechanism.
They’ve also created a molded plastic lock bracket that you can use to stow the lock in your bike’s main triangle.
The other pieces weigh as thus: front skewer 84g, rear skewer 93g, top bolt 40g, seatpost clamp 117g (with all the shims). The top bolt works with 1 1/8” upper-race headsets. They replaced parts weighing 58g, 67g, 33g, and 22g, respectively. The seatpost clamp comes with shims, so it can work with pretty much all round seat tubes. The lock bracket also come with shims; the bracket and the two bolts for it weigh 41g.
They all set up as easily as the parts they’re replacing. The only thing you should do is grease the threads on the install. You could take the conical springs off the quick releases you just removed and re-install them onto the Pinhead skewers. If you’re installing and removing wheels regularly, or expect to do so, the springs would help center the skewers, just as they do with standards quick releases.
The centerpiece of this set is the lock. Safe locks these days are generally pretty heavy, and reducing weight here makes your bike or bag lighter. Still 628g not light and it’s not small. For elementary school kids, the lock is almost certainly too big to fit inside their bike’s main triangle, so they’ll need to carry it, have a parent carry it, or leave it at school. For reference, the lock barely fits inside the main triangle of a 44cm road frame, if the water bottle cage is removed—so you’ll have to choose between water and the lock. So, you’ll need a space inside the frame of at least 31cm to make it work.
The lock fits around most posts and racks and small fences we’ve come across. If you have the Ultimate kit, or some other wheel securing means, the wheels are already locked in place, so there’s need to lock a wheel and the frame together. All the same, it does provide at least peace of mind for us to lock the front wheel, and we found we could lock both together and a post in many situations. When we couldn’t, we didn’t worry.
The one thing the Pinhead lock doesn’t seem to work with is the vertical support posts found on building scaffolding in New York City. Sadly, we have an almost irrational love of locking bikes to this kind of post. They’re so big and so strong that we figure no thief would care to battle it to get our bike.
The locking mechanism takes a little getting used to. It is spring-loaded, which means it’s always in the locked position, and the fork tip-looking hook that mates with it can’t be forced down on it to engage the lock without the key turned a quarter-turn counterclockwise. Likewise, it usually takes us a try or two to get the key’s pins lined up with the postholes on the lock. Not always easy, especially when fidding around in the dark.
Kids practiced on the lock mechanism. There is some effort to get the key into place and a little coordination to engage the pins and remember to turn the lever counter-clockwise. It never seemed super-easy, but they were able to get the hang of it. The difficulty is mainly getting a feel for when the pins are engaged. Adults seem to get the knack a good bit faster.
There’s much to like with the Pinhead setup. By keying everything identically, securing the bike gets much easier. The only limitations were the slight difficulty of using the lock mechanism and carrying it on small bikes. It may or may not work for kids; age and size seem to matter most. It could easily work for adults.