Hacking my “smart” toothbrush

This was an enjoyable read. My GE fridge uses RFID for keeping track of when to change the water filter. This isn't really an area I'm familiar with but I'm curious how much I would be able to figure out with the right tools.

Great article, the most interesting part of which is that you can lock your self out of your toothbrush head after three wrong password attempts. I didn't dig into the data sheet for the NFC chip very deeply, but I imagine that it's just the default that the chip ships with. Or maybe Philips really wants that $25 for a new toothbrush head. :-)

EDIT: nope, not the default. From the data sheet, last sentence:

"To prevent brute-force attacks on the password, the maximum allowed number of negative password verification attempts can be set using AUTHLIM. This mechanism is disabled by setting AUTHLIM to a value of 000b, which is also the initial state of NTAG21x."

So Philips went out of their way to secure that toothbrush head. That's reassuring.

I have one, but it never occurred to me to want to hack it.

"But how do you know when it's time to change the brush?"

Well, how about when it starts getting soft?

How about when the blue part goes away, as documented? :-) I've used a Sonicare for, what, ten years or more? And I don't think I've ever seen an indication that the NFC is communicating anything to me. That's not to say that it isn't, but if I'm going to ignore something[0] and replace the head when I damned well please, I just ignore the blue part of the bristles. I could probably adjust my behavior to ignore whatever flashing LED the NFC sets off, but after so many years I'm just going to continue ignoring what I always have.

[0] I'm either easy on toothbrush heads, or Philips is lying, because when the indicator says "buy a new head" it still has plenty of life IMO. Bristles straight and tall, just like a new one, but no blue left being the only difference between that and new. So I ignore it and get a new one when the bristles go a little wonky.

It works happily with a brush head without NFC. That was the first thing I tried with my new toothbrush.