By Utsav Gupta, electrical engineer and member of the informal freelance collective
Why this crossed our desks: Lego Smart Bricks sit at the heart of Lego’s Smart Play System, which uses sensors, lights, and sounds to add interactivity to play. The Smart Play system was announced at CES 2026 and was one my personal highlights of the show. I got some play time on Luke’s “Red Five” X-Wing and was impressed by the feature set of the brick given its small size and battery. The bricks brought me back to childhood, when I’d spend hours upon hours building and playing with new sets. If I were a kid, I’d be stoked to play with these!
At CES, Lego launched three sets with the Smart Play capability with shipping beginning on March 1. I signed up for the pre-orders as soon as I found out and knew, going in, that a teardown was in the books. After all, the Lego Group is well known for their outstanding engineering and manufacturing processes. I expected a similar level of detailed engineering effort went into these bricks and was eager to check out internals.
<aside>
The Smart Play System consists of Smart Bricks (1), Smart Tags (2), and Smart Minifigures (3). The tags and minifigures are passive devices that trigger interactive responses when in close proximity with the brick. The bricks are the brains of this system, and include a tiny PCBA-powered from a Li-ion battery. The bricks are charged wirelessly using the included Smart Charger (4). Lego claims that the bricks provide up to 45 minutes of play time after a 3-hour charge.
The SMART Bricks, Tags, and Minifigures are fully backward compatible with all existing Lego sets. At the time of writing, Lego isn’t directly selling the Smart Play platform — you need to buy one of the Smart Play All-In-One sets to receive the tags, bricks, and minifigures. After you’ve bought the Smart Play accessories, you can combine them with the Smart Play Compatible sets to enable the full play experience.
I bought one of each: the Throne Room Duel and A-Wing all-in-one set and the Luke’s Landspeeder Compatible set. So far, I’ve built up the A-Wing shown here and am working on the Throne Room set.
</aside>
<aside>
For context, I’ve marked each face with letters from A to F, in order from top, left, front, bottom, right, and back. FACE A is made of a clear plastic with a frosted surface, and snaps into an opaque, black housing. An additional transparent window (5) on FACE B exposes an LED and a photodiode to the outside world. A number of vents (6) are visible from but not exposed to the top layer.
A close look at FACE A shows that the location I previously identified as vent (6) is actually solid plastic, and the vents are located on either sides of it (7). The purpose of the vents is unclear at the moment but maybe the teardown will shed some light. The existence of these vents may mean that this product isn’t waterproof.
Smart Bricks retain the familiar 2x4 stud brick form factor, although with a 66% increase in height. Wireless connectivity is a recurring theme in the Smart Play System. The bricks use near-field magnetic coupling to detect tags or minifigures in close proximity. While LEGO advertises a detection distance of 1 cm, in my testing, I found that this distance varies depending on what face is closest to the tag.
Lego also developed a custom mesh protocol on top of BLE, called BrickNet, to allow multiple bricks to communicate with each other.
</aside>
<aside>
Minifigures are a core part of the Lego ecosystem and might be one of the most identifiable toys in the world. With the Smart Play System, Lego has introduced a unique aesthetic and character to each minifigure. A Smart Minifigure can be identified by a circular motif on the back, with light and sound icons inside the circle (8). Aside from this, the external appearance of the minifigures remains unchanged.
A side-by-side lateral cross-section of a regular minifigure (9) and a Smart Minifigure (10) reveals a key difference. The Smart Minifigure contains two flex coils, one in the front and the other on the back. These coils encode the particular light and sound data for a given minifigure. Once a Smart Brick is in close proximity to the minifigure, it detects the coil and knows the corresponding audio and light pattern it needs to generate.
The Smart Tags are functionally identical to the minifigures and also contain a flex coil embedded inside them. A sticker on the outside (11) depicts the relevant set, toy, or scene the tag belongs to. I decided to peek at the flex coil of Luke’s Landspeeder tag. I attached a coarse grinder bit to my rotary tool and made several horizontal passes on the face of the tag, essentially mimicking a surface grinder.
After several minutes of grinding, I could see the coil embedded inside the plastic. The rectangular pillars (11 and 13) and circular posts (12 and 14) might be used as locating features during the overmolding process. I also noticed an additional square (15) and couldn’t tell its purpose. I shined a flashlight from the bottom side to see if this is connected to a circuit or a structural part, but I didn’t see anything else. The flashlight did reveal the entire coil.
<aside> 💡
Let me know if you have an idea what this mystery square represents!
</aside>
</aside>
<aside>
The brick’s black outer housing is securely connected to the top clear housing using tabs. There’s no obvious way to disconnect the two without breaking the bottom housing. So I grabbed my pliers and went to town on FACE C of the bottom housing, and also ended up damaging part of FACE E.
The intact part of the bottom housing, on the right, shows one of the snap hooks (16) for the transparent window on FACE B. The wide middle line ending in a C aids in plastic flow during molding. And on the right, we see a gate location (17). It’s interesting to see the gate offset to the right side. Maybe the lifter for the snap hook (16) got in the way.
We get a first look at the internals after removing the bottom housing. The top housing connects to another clear, plastic middle housing using snap hooks (20). The entire middle housing is wrapped in multiple nonintersecting coils of copper wire (18) . I feel for the engineer who had to manually create the proof-of-concepts for this design.
I accidentally broke one of these coils (19) while prying open the outer housing. On FACE B, we see an edge-mounted LED (22) on the top side of the PCBA and a photodiode (23) on the bottom side.
The copper coils are attached to the gold-plated PCBA edges using thermosonic compression in a process called wire bonding (21). The copper coils of the brick form an inductive loop on each face. These loops can detect changes in the local magnetic field that occur when I bring a tag (or minifigure) close to the brick. The face with the highest change in the magnetic field is always the closest to the tag. The amount of change in the magnetic field is also driven by the orientation of the coils with respect to each other.
In other words, the Lego engineers found a very clever way to use the magnetic field as a local positioning system! And they further exploited the physics to detect local motion to trigger the lights and sounds on the brick. You can see this effect in the video at the top of this page, between 6 seconds and 11 seconds.
Pulling the joystick back raises two plastic arms on each side of the brick. The arms must have some amount of metal embedded inside, which triggers changes in the magnetic field, which are then detected by the brick and result in the pew-pew-pew sounds.
</aside>