This engineer was curious to figure out why the Bluetooth tracker for his keys had abruptly gone deceased. Then he remembered a few-year-back mishap…

My various Tile trackers—a Mate attached to my keychain (along with several others hidden in vehicles)—and a Slim in my wallet, have “saved my bacon” multiple times over my years of using them, in helping me locate misplaced important items.

But they’ve been irritants as well, specifically in relation to the activation buttons and speakers built into them. Press the button, and the device loudly plays a little ditty…by default, it also rings whatever smartphone(s) it’s currently paired with. All of which is OK, I guess, as long as pressing the button was an intentional action.

However, when the keychain and/or wallet are in my pockets, the buttons sometimes also get pressed, as well…by keys or other objects in my front pocket, credit cards in my wallet, or sometimes just my body in combination with the pants or shorts fabric. That this often happens often when I’m unable to easily silence the din (while I’m driving, for example) or at an awkward moment (while I’m in the midst of a conversation, for example), is…like I said, irritating.

Silence isn’t always blessed

I eventually figured out how to disable the “Find Your Phone” feature, since I have other ways of determining a misplaced mobile device’s location. So my smartphone doesn’t incessantly ring any more, at least. But the tracker’s own ringtone can’t be disabled, as far as I can tell. And none of the other available options for it are any less annoying than the “Bionic Birdie” default (IMHO):

That said, as it turns out, the random activations have at least one unforeseen upside. I realized a while back that I hadn’t heard the tune unintentionally coming from the Tile Mate on my keychain in a while. After an initial sigh of relief, I realized that this likely meant something was wrong. Indeed, in checking the app I saw that the Tile Mate was no longer found.

My first thought (reasonable, I hope you’ll agree) was that I had a dead CR1632 battery on my hands. But to the best of my recollection, I hadn’t gotten the preparatory “low battery” notification beforehand. Indeed, when I pulled the coin cell out of the device and connected it to my multimeter’s leads, it still read a reasonable approximation of the original 3V level. And in fact, when I then dropped the battery into another Tile Mate, it worked fine.

A rough-and-tumble past

So, something inside the tracker had presumably died instead. I’d actually tore down a same-model-year (2020) Tile Mate several years back, that one brand new, so I thought it’d be fun to take this one apart, too, to see if I could discern the failure mechanism via a visual comparison to the earlier device.

At this point, I need to confess to a bout of apparent “senioritis”. This latest Tile Mate teardown candidate has been sitting on my bookshelf, queued up for attention for a number of months now. But it wasn’t until I grabbed it a couple of days ago, in preparation for the dissection, that I remembered/realized what had probably initiated its eventual demise.

Nearly four years back, I documented this very same Tile Mate’s inadvertent travel through the bowels of my snowblower, along with its subsequent ejection and deposit in a pile of moist snow and overnight slumber outside and to the side of my driveway. The Tile Mate had seemingly survived intact, as did my keys. My Volvo fob, on the other hand, wasn’t so lucky…

Fast-forward to today, and the Tile Mate (as usual, and as with successive photos, accompanied by a 0.75″/19.1 mm diameter U.S. penny for size comparison purposes) still looks reasonably robust, at least from the front:

Compromised environmental barriers

Turn it around, on the other hand…see that chip in the case above the battery compartment lid? I’d admittedly not noticed that now-missing piece of plastic before:

Arguably, at least theoretically, the lid’s flipside gasket should still preclude moisture intrusion:

But as I started to separate the two case halves:

I also noticed cracks at both battery compartment ends:

Again, they’re limited to the battery area, not intruding into the glue-reinforced main inner compartment where the PCB is located. But still…

And what’s with that additional sliver of grey plastic that got ejected during the separation?

As you may have already figured out, it originated at the keyring “hole”:

After it initially cracked (again, presumably as a result of the early-2022 snowblower debacle) it remained in place, since the two case halves were still attached. But the resultant fracture provided yet another environmental moisture/dirt/etc. intrusion point, albeit once again still seemingly counteracted by the internal glue barrier (perhaps explaining why it impressively kept working for four more years).

Here’s a reenactment of what the tracker would have looked like if the piece had completely fallen out back then:

See, it fits perfectly!

Non-obvious defects (at least to my eyes)

Here’s what this device’s PCB topside looks like, flush with test points:

Compared to its brand-new, same-model-year predecessor, I tore down nearly five years ago:

Same goes for this device’s PCB underside, notably showcasing the Nordic Semiconductor nRF52810 Bluetooth 5.2/BLE control SoC, based on an Arm Cortex-M4, and the associated PCB-embedded antenna along one corner:

versus the pristine one I’d dissected previously:

I don’t see a blatant failure point. Do you? I’m therefore guessing that moisture eventually worked its way inside and invisibly did its damage to a component (or few). As always, I welcome your theories (and/or other thoughts) in the comments!

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

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