Amazon’s Smart Plug: Getting inside requires more than just a tug

Amazon doesn’t want naïve consumers poking around inside its AC-switching devices. This engineer was also thwarted in his efforts…initially. The post Amazon’s Smart Plug: Getting inside requires more than just a tug appeared first on EDN.

Electronics Jan 6, 2026 0 4 Add to Reading List

Amazon’s Smart Plug: Getting inside requires more than just a tug

Amazon wisely doesn’t want naïve consumers poking around inside its high-voltage AC-switching devices. This engineer was also thwarted in his exploratory efforts…initially, at least.

Early last month, within a post detailing my forced-by-phaseout transition from Belkin’s Wemo smart plugs to TP-Link’s Kasa and Tapo devices, I mentioned that I’d originally considered a different successor:

Amazon was the first name that came to mind, but although its branded Smart Plug is highly rated, it’s only controllable via Alexa. I was looking for an ecosystem that, like Wemo, could be broadly managed, not only by the hardware supplier’s own app and cloud services but also by other smart home standards…

A curiosity-satisfying return-on-(minimal) investment

Even though I ended up going elsewhere, I still had a model #HD34BX Amazon Smart Plug sitting on my shelf. I’d bought it back in late November 2020 on sale for $4.99, 80% off the usual $24.99 price (and in response to, I’m guessing, per the purchase date, a Black Friday promotion). Regular readers already know what comes next: it’s teardown time!

Let’s start with some outer box shots, as usual (as with subsequent images), accompanied by a 0.75″ (19.1 mm) diameter U.S. penny for size comparison purposes:

Note that, per my prior writeup’s “specific hardware requirement that needed to be addressed,” it supports (or at least claims to) up to 15A of current:

Input: 100-120V, 60 Hz, 15A Max
Output:
- 120V, 60 Hz, 15A, resistive load
- 120V, 60 Hz, 10A, inductive load
- 120V, 60 Hz, 1/2 HP, motor load
- 120V, 60 Hz, TV-5, incandescent
Operating Temperature: 0-35°C
IP Rating: IP30

thereby being capable of power-controlling not only low-wattage lamps but also coffee makers, curling irons, and the like:

See that translucent strip of tape at the upper right?

Wave buh-bye to it; it’s time to look inside:

Nifty cardboard-based device-retention mechanism left over at the bottom:

The bottom left literature snippet is the usual warranty, regulatory and other gobbledygook:

The one at right is a wisp of a quick-start guide:

But neither of them, trust me I already realize, is the fundamental motivation for why you’re here today. Instead, it’s our dissection subject (why was I having flashbacks to the recently viewed and greatly enjoyed 2025 version of Frankenstein as I wrote those prior words?):

Underneath the hole at far left is an activity-and-status LED. And rotating the smart plug 90°:

there’s the companion switch, which not only allows for manual power control of whatever’s plugged into it but also initiates a factory reset when pressed and held for an extended period.

Around back are specs-and-such, including the always-insightful FCC ID (2ALBG-2017), along with the line (“hot”) and neutral source blades and ground pin (Type B NEMA 5-15 in this case):

In contrast to its left-side sibling, the right side is comparatively bland (i.e., to clarify, there’s nothing under the penny):

as are the bottom:

and the top, for that matter, unless you’re into faintly embossed Amazon logos:

Tenuous adhesive

My first (few…seeming few dozen…) attempts to get inside via the visible seam around the backside edges, trying out various implements of destruction in the process, were for naught:

Though the efforts weren’t completely wasted, as they motivated me to finally break out the Dremel set that had been sitting around unused and collecting dust since…yikes…mid-2005, my Amazon order history just informed me:

and which delivered ugly but effective results (albeit leaving the smart plug headed for nowhere but the landfill afterwards):

First step: unscrew and disconnect the wire going from the front panel socket’s load (“hot”) slot to the PCB (where it’s soldered):

Like I said before…ugly but effective:

At the top (in this photo, to the left when originally assembled) are the light pipe that routes the LED (yet to be seen but presumably on the PCB) output to the front panel, along with the mechanical assembly for the left-side switch:

You’ve already seen one top view of the insides, three photos ago. Here’s another, this time standalone and rotated:

And here are four of the five other perspectives; the back view will come later. Front:

Left side, showing the PCB-mounted portion of the switch assembly:

Right behind the switch is the outward-pointing LED whose location I’d just prognosticated:

Right side:

And bottom:

Electron routing and switching

Onward. The ground pin from the back panel routes directly to the front panel socket’s ground slot, not interacting with any intermediary circuitry en route:

You’ve probably already noticed that the “PCB” is actually a three-PCB assembly: smaller ones at top and bottom, both 90°-connected to the main one at the back. To detach the latter from the back chassis panel requires removal of another screw:

Houston, we have liftoff:

This is interesting, at least to me. The neutral wire is attached to its corresponding back-panel blade with a screw, albeit also to the PCB at other end with solder:

but the line (“hot”) wire is soldered at both ends:

This seemingly inconsistent approach likely makes complete sense to those of you more versed in power electronics than me; please share your thoughts in the comments. For now…snip:

Assuming, per my earlier comments, that you’ve already noticed the three-PCB assembly, you might have also noticed some white tape on both sides of the mini-PCB located at the bottom. Wondering what’s underneath it? Me too:

The answer: not much of anything!

What’s the frequency, Kenneth?

(At least) one more mystery to go. We’ve already seen plenty of predictable AC switching and AC-to-DC conversion circuitry, but where’s all the digital and RF stuff that controls the AC switching, along with wirelessly communicating with the outside world? For the answer, I’ll direct your attention to the mini-PCB at the top, which you may recall initially glimpsing earlier:

What you’re looking at on the other side is the WCBN4520R, a Wi-Fi-plus-Bluetooth Low Energy module discussed in-depth in an informative Home Assistant forum thread I found.

Forum participants had identified the PCB containing the module as the WN4520L from LITE-ON Technology, with Realtek’s RTL8821CSH single-chip wireless controller and Rockchip Electronics’ RKNanoD dual Arm Cortex-M3 microcontroller supposedly inside the module. But a different teardown I found right before finalizing this piece instead shows MediaTek’s MT7697N:

A highly integrated single chip offering an application processor, low power 1T1R 802.11 b/g/n Wi‑Fi, Bluetooth subsystem and power management unit. The application processor subsystem contains an ARM Cortex‑M4 with floating point unit. It also supports a range of interfaces including UART, I2C, SPI, I2S, PWM, IrDA, and auxiliary ADC. Plus, it includes embedded SRAM/ROM.

as the main IC inside the module, accompanied by a Macronix 25L3233F (PDF) 32 Mbit serial flash memory. I’m going with the latter chip inventory take. Regardless, to the left of the module is a visible silhouette of the PCB-embedded antenna, and there’s also a SMA connector on the board for tethering to an optional external antenna, not used in this particular design.

And there you have it! As always, sound off with your thoughts in the comments, please!

—Brian Dipert is the Principal at Sierra Media and a former technical editor at EDN Magazine, where he still regularly contributes as a freelancer.