Switch from 770 to Tandem

Have you switched from the 770 to Tandem or visa versa? What was your experience?

Thank you

Hi @doug . I’ve been using Tandem’s T-Slim for years and love it. I can’t give comparison with the 770 but wanted to let you know people who switch do tend to find the full process takes longer. And T-SLIM had to be charged rather than using batteries. Personally I prefer that, aND it doesn’t take long - and my car charger or portable “brick” work just as well as the wall socket.
I don’t mean to start you off on a negative but it seems people are unexpectedly surprised by the differences. I’ve long since gotten used to them so don’t think about them any more, and my experience with T:Slim/Dexcom Control IQ more than makes up for them.
FWIW there’s a T-Simulator app that let’s you get a virtual feel for the basic pump.
Wishing you the best if you’re considering changing either way.

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I switched from 670 to t:slim X2 this year. It’s been great. The 670 and 770 are the same pump except that the 770 has an app (which allows you to see your pump status on your phone, uploads pump data to a remote server automatically, and allows you to update your pump software at home whenever there’s a new release). The t:slim has an app that does all that, too.

  • The Dexcom sensors are far more accurate than the Guardian 3. They’re also easier to insert and last longer. And the adhesive doesn’t irritate my skin the way the Medtronic oval tape did.

  • It’s a relief to have a pump that inherently trusts the CGM instead of one that requires fingerstick confirmation for everything, multiple calibrations per day, alarms at the drop of a hat, etc. With the Tandem pump, you technically never have to calibrate at all. (I do calibrate daily, just to be sure, but after the first day, the sensor has always been spot on for me. Even the first day usually goes well, although a couple of times I’ve needed to give it 12 hours or so to get properly on track. Still much better than I had with the Medtronic sensors, which always took 12 hours and at least 3 calibrations to get on track, even at its best.)

  • The algorithm is better at keeping me in good control, and it will even give me an automatic correction bolus (above just adjusting the basal) if it’s been an hour since my last bolus and I’m still running high.

  • The phone app (which I know the 770 has and the 670 doesn’t, so I can’t compare) is nice to have. The Tandem app gives me a graph of my CGM values along with basal rates and boluses. It also gives the current pump settings, status information, alerts, etc. The Dexcom G6 app keeps the CGM graph and latest reading in my phone’s notifications, so I can always see that with a single gesture. The Dexcom Clarity app gives me broader stats like my average CGM reading, time in range, etc. I’m told they’re working on FDA approval for a remote bolus feature where you could program bolus delivery from your phone. No idea if or when that might be approved, but it would be nice.

  • The user menus on the pump itself are better organized than the Medtronic ones. The options to stop delivery or start an activity (sleep and exercise have special temporary target BG ranges) are right at the top. The bolus wizard has its own dedicated button on the main screen. There’s a button off to the side that always takes you directly back to the main screen if you’ve been digging through submenus.

In the broader scale, you’ve got the pump adjusting the basal based on your CGM readings, so that general background stuff is much the same. And I’m using the exact same infusion sets.


  • I like having a touchscreen, but the Tandem one is finicky. You have to touch the buttons exactly where it expects or else it turns the screen off and forces you to go through the unlock sequence again. And the part of the touchscreen I have the most trouble with (center of the bottom edge) is part of the unlock sequence.

  • The bolus wizard is annoying. You have to confirm and re-confirm everything multiple times before it will actually start delivery. And just when you think you’re done it asks you to confirm again.

  • I don’t like the cartridge system. Medtronic’s reservoir is compact and built right in to the syringe. Tandem requires you to assemble the syringe, draw up the insulin, pull excess air out of the cartridge, then inject the insulin to fill the cartridge. But you can’t see what you’re doing because the cartridge is opaque. And it can be a little different depending on exactly how the syringe hits the fill port. There’s always an extra drop of insulin that comes out when you remove the syringe from the fill port. And the cartridge has a “tail” that serves as the connection to the infusion set, so you’ve got this bulky connector bead two inches into the tubing.

  • The Dexcom sensor generates a lot more waste. Instead of a reusable insertion device, every Dexcom sensor comes with its own insertion device. A single-use hunk of plastic the size of an electric shaver. Which technically is medical waste because somewhere in there is a little needle that penetrated your skin for a fraction of a second.

  • The Tandem delivery system is louder than Medtronic’s. It’s not that loud (and I do have hypersensitive hearing), but there’s an audible whir whenever it’s working.

  • The Tandem pump also has beeps that you can’t turn off. Medtronic lets you silence everything except alarms. Tandem will beep or vibrate every single time you press the touchscreen. It’ll beep every time a bolus starts. It’ll beep every time a bolus finishes. It’ll beep when the CGM starts. It’ll beep… You get the idea.

  • Tandem’s weird use of colons and lowercase letters for proper names (t:slim, t:connect, etc.) is mildly irksome and I don’t know why they do that.

Overall, I’m really happy I made the switch. I know others have had a different experience. But that’s how it’s been for me. I hope this helps. AMA.

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Here’s what the connection looks like:

Forgot to mention:

Medtronic uses a AA battery. You can use a lithium battery that lasts about 2 weeks. I used rechargeable NiMH batteries. Those last about a week, but if you keep a couple of spares on you, it’s not hard to swap out and recharge as necessary. Cheaper and less waste.

Tandem has an internal rechargeable lithium battery. About twice a week, when the battery level drops to 40-50%, I plug it in for half an hour or so when I’m sitting next to an outlet. You can also just plug it in when you disconnect to take a shower. It charges pretty quickly.

It’s not a big deal either way, but I find it’s less hassle to plug in and top off the internal battery than it was to fumble off the battery cap, deal with the alarm, swap batteries, get the battery cap back on, and hope that the changeover didn’t happen during a scheduled CGM update (which did cause signal loss a couple of times). I had to get a spare battery cap, too, because the metal piece that makes it work kept falling off.

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Since the difference between the 670 and 770 is the app, you might do a search for “670” on the forum: there has been lots of comparison between the 670 and T-SLIM - much of it involving CGM accuracy - but there are comments on the basics of the pumps as well.

Thanks for the info on the pump. Very helpful. Have you gone through airport TSA with it? Can it handle the body scan machine?

Thank you for the helpful detail. Have you gone through airport TSA with it? Can it handle the body scan machine?

You need to remove it for radiology. When I go through building security I explain that it’s a sensitive medical device. I haven’t flown in ages but I believe there is documentation you can carry with you - TSA agents are supposed to recognize them but…
Same applies to Dexcom’s CGM: Dexcom will replace sensors that don’t last the full 10 days they are designed for, and that includes if you have to remove one for a test (on the rare occasions I’ve had scans done I scheduled them for say 10 - wish I’d known about that earlier!).

Both the Medtronic and the Tandem pumps come with the same instructions. Click through for more specifics, but in summary:

You can go through a metal detector with no problem, but avoid radiation, including body scanners. If you want to go through the scanner, you should disconnect the pump (and remove the Guardian 3 sensor from your body).

Likewise, Dexcom says metal detectors are fine but body scanners haven’t been tested and could theoretically be a problem, so they recommend avoiding those.

Avoid putting equipment through the luggage scanner, as well.

TBH, you get more radiation just from being in the upper atmosphere on an airplane than you do from the body scanner. But I’m not taking chances with the piece of technology that my life literally depends on. I’ll go through the metal detector if TSA allows it, and that’s no problem. Unfortunately, TSA doesn’t let you choose. (Which makes sense because it could make it easier to hide something.) So most of the time I have to get the full patdown. It takes longer and it’s exhausting when you’ve also got fibromyalgia. But it doesn’t happen that often, and it’s the price I pay for the convenience, flexibility, and BG control of having a pump.

Thank you for the in-depth review. I am currently on a 770, but have been wanting to switch to Dexcom for a while. just for the trusting CGM. The 770 is way better than the 670, but still believe a different pump would help me be in better control.

I have been flying for years, and a few times a year, and I always show them my insulin pump, and I go thru one of the scanners. They always used to have me touch my pump, and then swab my hands with something, and put it in a scanner. They haven’t been doing that every time I have flown in the past year. I have never noticed any issue with my pumps after going throw airport security, where ever it has been.

Thanks for all of the info. As for air travel - I’ve gone through both types of scanners with no issues.
I’m on the 770 now and don’t like it. Too many alerts - especially for checking bg. I feel that I am required to adapt to it rather than it to me, and that is unacceptable given the price. In my mind, the device works about 70% of the time. If my mobile phone had the same performance, I’d get a new one. Another peeve is the initial calibration time for a new sensor: 1/2 a day and multiple finger sticks, along with a day of high BS unless I’m really on top of it. Dexcom looks darn good in that regard.

Like I said, there’s very little radiation from the body scanners and I expect it’s probably fine. But all three manufacturers specifically say not to chance it. I’m sure they’re just being extra cautious. But, again, my life depends on these devices functioning properly, so extra caution is not unreasonable.

I have/had the same the same inaccuracy the first day with the dexcom too. I would suggest you get try to get a trial of the dexcom before commiting. First day inaccuracy is fairly common on g5/g6 medtronic and Freestyle libre2 for me.

I traveled as recent as June 5th and they made me take the pump out, rub it with my hands and then tested my hands with a cotton swab… as usual. I’ve never gotten away with not getting tested lol. I don’t mind, I already know the drill. I’ve always gone thru the body scanner and nothing has happened to my devices. Just wanted to share my experience.