Model difference between SM2 and SM3

Hello Everyone! I’m an electrical engineer in central New York and just installed a sense energy monitor at my home yesterday. I’m very excited about it and learning more about ways that I can improve my energy usage throughout the day/week…

The sense unit that I’m using is a model SM2 (I bought used). It is my understanding that the current hardware being sold is SM3 and that it may have been around for a while. I searched a lot before buying to try to find the difference between SM2 and SM3 but I couldn’t find anything. I wasn’t able to ask here prior to buying since I didn’t have an account yet. I figured the functionality is probably similar otherwise I’d find some comparisons…

I would like to know if there are any known limitations of the SM2 as compared to current SM3 that I should be expecting. Is it less accurate? Does it consume more power? Is it not able to connect to something? I’m guessing this has probably been discussed in the forum closer to the launch of SM3 but it seems it has a 1year memory so it is probably out of that window…

Thanks for any information on this!

I don’t know the designations SM2 and SM3, but I do know the early Sense monitors used a TI ADC/DSP combo, while the newer hardware uses NXP chips. I don’t think there is any significant difference in functionality though the TI-based units might be a little more stressed on SPI based DMA, and might run a little tighter on software task deadlines. There is certainly no big difference in the persistent memory as you suggest.

As an EE, you would probably appreciate a blog on Sense’s main firmware guy, here:

Ps:Take a look at his linked blog to get an idea of the challenges within the Sense HW.

pss: Here’s a teardown of the TI-based hardware.

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Where does on check to find if SM2 or SM3.

Purchased on Amazon Prime Day so I assume it should be newer unit.

Hello kevin1,

Thanks for the information provided above. The firmware assembly hacks described in the blog sound like fun stuff :slight_smile: I also reviewed the teardown pics provided. It seems that they are for a model even older than the one I have (the pics are for SM1). Having just installed the unit and since I’m not having any issues I think I won’t try to open it up to look at the chips that I have. Good to know that these older versions may have no significant limitation known as compared to current hardware.

Thanks again! Also, if anyone else reading knows of any significant difference between SM2 and SM3 please let me know.

@MoonDog , welcome to the world of Sense ! Nice to have another fellow EE online.
Just revisited the teardown, and you nailed it - that’s an SM1.
@Beachcomber, I don’t think there are any easy ways to tell SM versions apart by date sold or external appearance AFAIK. Sense has chosen to keep functionality exactly the same so they don’t distinguish. There is one external clue to the different makes without doing your own teardown - the MAC address. I have two Sense monitors with very different MAC addresses.

My main one, with a MAC that starts a4:d5 OUI ids to Texas Instruments
The second one, with a MAC that starts dc:ef OUI ids to Murata Manufacturing.

I’m guessing those correspond to SM2 and SM3, but who knows.

Well, mine starts with 74:7a:90 :man_shrugging:t3:

The reason I asked is I see my Sense showing up as Sense-N112030021 in the WiFi pic I posted on another thread where @DevOpsTodd pic showed his as N113…. and he’s clearly had his for a long time prior to me (again, purchasing on Amazon Prime Day this year).

@Beachcomber I haven’t had my Sense monitor for long:


I think the Sense monitor uses its serial number for the clientID.

You can paste your MAC into this site (among many) and have it ID the manufacturer of data the WiFi chip.

So, I believe at least SM2s and SM3s have the model number written on the red unit itself… You should be able to see it if you give a good look around. Sometimes the units for sale on ebay have pictures of it depicting (mostly) SM3.

Again, I’m guessing the difference between models isn’t significant but would like to know if it is :slight_smile:

Guess Amazon had old stock and you purchased it directly :man_shrugging:t3:

I’m not sure what you mean by that. I have the SM3 and I purchased it from Amazon.

And so there is no misunderstandings, I am referring to these numbers as to “old stock”, not version numbers.

Those numbers as @kevin1 mentioned are serial numbers. If you go to My Home → Sense Monitor you will see the serial number is the same number you are highlighting. You can also verify this serial number with the label on the box as shown below.

If you want to know what hardware version you have look at the box that your Sense came with and it will be on the label as SM2 or SM3. This is also on the device as many have pointed out. I have an SM3. This should answer your question:


It doesn’t appear that serial numbers are sequential because I find it highly unlikely that Sense has manufactured over 1 million monitors. Could the 2 vs 3 (as the 4th character of the serial) be the difference between the SM2 and SM3, only a Sense employee could tell us or a poll of what people know they have. As for Amazon stock, that just depends on the demand from your local"ish" warehouse.

I think the OP is asking what the specific difference between the SM2 and SM3 is. As @kevin1 mentioned there’s obviously a hardware difference because of the use of different internals that we can easily see by the radio manufacturer and hardware MAC.

Maybe @RyanAtSense could provide information or insight into the exact differences between the SM2 and SM3?

My SM2 has no 2 in the serial number

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My SM3 (bought from Amazon the last week of Nov 2020) has a 2 in the fourth position of the SN.

I wonder if all SM2 start with the letter M and SM3 N🤷🏼‍♂️

Can clear up some of the questions here.

There’s no user-facing functional difference between model revisions of the Sense monitor. The differences are only in the BoM and were made for a variety of reasons.


Thanks for the clarification, @JustinAtSense .

That is what I was hoping to hear!!

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