This would actually mean, it is a good chance that it is a Low frequency 125kHz card.
HOWEVER… before we count our 
I looked up Siemens and there is conflicting information on frequencies.
I did find they definately use
13.56MHz
ISO 15693, MIFARE classic (ISO 14443 A)
that’s how Siemens wrote it…
But I would have thought the TagInfo app would have read this…
Did you try holding the access card
- On the back of phone
- with NFC turned on
- Screen turned on
- Running TagInfo read
- Moving slowly/ placing card on different orientations, particularly perpendicular to the NFC antenna ( google your make and model for NFC antenna) or check out this WIKI
I did find mention of 125kHz and EM4100, (which is compatible with LF side of NExT), but nothing concrete; more hearsay and conjecture which would make sense if
Siemens used to use 125kHz in their older tech, which you could be dealing with.
- Next for you my friend, I would suggest you try the TagInfo steps above if you haven’t already.
- Like @turbo2ltr said Let us know what City you are in, There might be somebody nearby that can help you out with a Proxmark.
- Again agree with @turbo2ltr Start being friendly with the security staff (but not in a creepy stalker way)
- Try and get you hands on a spare access card ( or “loose” yours get a replacement, and send your “lost” card to one of us for analysis)
- make enquiries, as to what system is in use
- If you were smart about it you could do both
- “Oh Noooo I’ve lost my card, could I please get a replacement… sorry to be such a pain. NOW TELL ME EVERYTHING ABOUT HOW THIS SECURITY SYSTEM WORKS”
- or a variation there of…
You could buy a Dangerous things RFID diagnostic card, but really if you were going to spend money on that, you might as well buy the NExT and get one for free included.