I’m planning on buying the nXT, and I’m wondering if once I program it, can I undo that and make it do something else? I’ve heard some NFC cant be reprogramed but some can? I’m just confused on how this works. Like lets for say I wanted to use it to unlock my phone, and I set it to unlock my phone when I scan it, all good. But now I want to use it to turn off my wifi, do I have to do something to the nXT or do I do that on my phone.
Yes, the xNT has user memory that can be reprogrammed over and over again. That said, let’s analyse your example;
When using your xNT with various devices, most access control systems only care about the UID or serial number of the xNT… this is read only and not reprogrammable. You program the UID into the device or door lock (or an infinite number of door locks) along with other UIDs the lock should open for, and that’s that. No programming of the xNT happens at all. Your phone unlocking example works like this. You could unlock infinite phones with your xNT.
Turning off wifi requires an NFC app on the phone like Tasker or NFC Trigger. Those apps typically read an NDEF record stored on the xNT in the user memory space. That record can only do one thing at a time… like launch a Tasker task or NFC Trigger script. Those apps can then do a series of things chained together, or not, or toggle actions based on the logic built into those apps and the configuration you have set up… but as far as the xNT is concerned, when used with NFC smartphones, only one NDEF message is processed (even though you could store more messages on the xNT).