Some info The app works on the LG Optimus V but it does not work on the Atrix 4G it keeps acting like it detects card data so I assume its reading from the second microphone. For the users asking New vs Old it does not work on the new readers. However cracking open the New reader and desoldering the board and wires then adding a 100ohm 1/8watt resistor inline seems to work well.
Droid X2 Did not work on a Droid X2 version 2.3.5. Get the bad read message. Tried various credit cards. Square worked just fine, even on a card that I have trouble with at the store. It would be nice to know what it thinks it got.
Red circle stays red, will not read cards, using a homemade reader, an actual credit card reader head direct wired to the mic terminals of the TRRS plug. May work with the square reader, but I don't know how to tell the old non encrypted one from the new one. Tried tweaking settings, still no luck. Update: I now have a generic reader, and it reads cards 2 out of 5 times with the app.
Didn't work at all for me on Acer A500 using various cards the SquareUp app can read easily. Every swipe failed with a, "bad read, try again" error.
Pretty inconsistent results (correctly reads ~10% of the time). Seems to work better with a faster swipe. I'm using a knock-off Square reader from china (via Aliexpress).
It doesn't work Moto G 1st and 2do generation. Always 'Bad read'. I tried with different settings without any result.
Removed a few debug statements that might leak info through logs, attempt to fix occasional NullPointer crash on Square dongle insert/remove.