A 2026 field guide to the three labels that get mixed together on a door: the reader-to-controller bus (Wiegand or OSDP) and the credential technology (for example NFC / MIFARE DESFire). Detailed OSDP how-to remains in the existing guides t=151 and t=152 — this thread does not repeat those wiring and configuration steps.
Complexity
Beginner to moderate as a planning read. Adding readers on a live access-control door is an access-control and cabling job, not a first Home Assistant project.
1. Wiegand — the legacy, one-way reader bus
SIA and almost every access-control vendor still describe Wiegand as the older reader interface: unidirectional data from the reader to the controller, typically with limited supervision. It is widely deployed and still sold, but it does not provide a rich, authenticated, bidirectional channel. If a door only has a Wiegand run, plan an upgrade path before you promise encrypted reader comms.
2. OSDP — the supervised, bidirectional alternative
OSDP (Open Supervised Device Protocol) is SIA's modern reader-and-device protocol, running as a bidirectional, supervised bus (commonly over RS-485). Public SIA comparison material contrasts it with Wiegand on a small set of practical factors (among them: direction of communication, supervision, and the ability to use a secure channel). The full SIA comparison guide is form-gated on their site; use the landing-page facts plus the existing Just Smart Homes OSDP threads rather than a copied vendor blog.
When you specify OSDP, also specify whether the door will use the secure channel, and whether the controller and reader firmware actually implement the same OSDP profile. See t=151 and t=152 for the forum's worked OSDP material.
3. NFC / DESFire — a credential, not a door bus
NFC and card families such as MIFARE DESFire describe how the tag and the reader talk in the air, and how keys and files are organised on the card. They are not a replacement for Wiegand or OSDP. A DESFire card can sit in front of a reader that then talks OSDP (or still Wiegand) back to the controller.
Mixing the terms causes bad procurement ("we want an NFC door, so we do not need OSDP"). Decide both:
- What credential will people present (card, fob, phone wallet / NFC, PIN)?
- How will the reader talk to the controller (Wiegand today, OSDP for new work unless the panel cannot do it)?
- Does the existing panel have native OSDP, a licensed OSDP port, or only Wiegand?
- Are the readers and the controller from a combination the vendor will support?
- Is the cable a genuine RS-485-capable run if you are moving to OSDP, or is it an old Wiegand loom that needs looking at?
- What happens at the door if the network or the smart-home hub is down? Access control should still follow the access-control system.
Readers, modules and re-cabling should be quoted in AUD against the panel you actually have. This thread does not invent a per-door price.
Official / existing reading
SIA: Open Supervised Device Protocol
SIA: OSDP compared with Wiegand (landing page; full guide is form-gated)
OSDP guide · OSDP follow-on
Researched from official documentation on 15 November 2026 (Australia/Sydney). This is a planning and how-to guide, not a claim that the exact hardware combination was assembled and tested on a live site. Please correct anything that has moved on.