I slipped my workspace ID card into the case for my iPhone 6s Plus, since I usually have my phone out when I get out of the elevator anyway. This works well, I wave my phone at the reader next to the door and it opens.

But I notice the Apple Pay screen comes up too when I do that.

Does that mean its NFC chip is the same as my ID card, and a clever app could emulate my card?

The iPhone does not currently allow access to the NFC hardware by any 3rd party app. It's unclear if or when this will change. Apple's own iPhone registers in the Apple store use a custom case to read Apple Pay, instead of using the built in NFC hardware.

NFC is a subset of RFID. Specifically it passive and uses the 13.26 MHz frequency that passive RFID can use. Passive RFID has two other frequencies that it may use. RFID was intended for longer range scanning, while NFC is intended for contact or very close scanning.

Your ID card may be NFC, or RFID using 13.26 MHz.

Do you think the Apple Pay widget would be triggered just by the frequency alone? Or do you think it detected some actual nfc data?

It just means it passed the anticollision and the reader was able to read out the tag identifier and select the tag.

Presumably the reader would do exactly the same if you waved a London Underground oyster card at it.

Edit:

I misread that it was apple pay screeen coming up on the phone, same reason though.

The anticollision the method by which the reader is able to determine the identifiers of all the tags in range (go read the specs on these if you like, they're kind of interesting...really!), so it selected each tag it found in turn, obviously one of which was your access tag which opened the door, it also selected the apple pay tag which would appear to be enough to wake your phone and get it ready for some apple pay action, but then stopped as it wouldn't have known what to do.

Yes, the frequency alone does trigger the Apple Pay screen. Though this is a vast oversimplification of what's going on, and I'm struggling to use the right technical RF terms to explain the interaction.

I personally hadn't seen this till this morning by putting my iPhone and WiiU gamepad together. It seems Apple did this to try and increase the speed of payments, possibly as a way to help spur adoption by keeping friction down wherever possible.

Google Wallet on some Android phones will wait for the connection to progress a little further between the phone and the other device/tag, activating only if it gets back the "this is a payment terminal" identifier. This likely is due to the wider use of NFC on Android where the communication needs to occur for the phone to know what application to notify.

Looking up more on this behavior, I did find someone else joking about their elevator accepting Apple Pay. Also seems Sony released an Android phone that also skips that initial check and launches into a photo app when it senses any NFC readers.

Couldn't find a way to disable this though, even after toggling "lock screen access" for Wallet. I'm surprised iOS 9.2 left no way to change this behavior as it is impacting some people's use of boarding passes or other non NFC based wallet items. This is happening when a combination optical scanner for QR codes and NFC reader is used.

That makes sense. Fascinating!