Registered as "EMCADS Server Port" for a remote-access product that no longer exists as a going concern.
IANA registers 3945 as emcads, "EMCADS Server Port", to a private assignee. EMCADS was the transport of a token-based secure remote-access gateway, but no protocol specification was ever published and the product is off the market, so nothing about its wire format or cryptography can be verified today. Treat the registration as a historical label. Listeners on 3945 in a modern estate are far more likely to be an unrelated application than EMCADS.
Do not expose
It was a gateway built to face the internet, but it is unmaintained and unpatched, which is exactly the combination that should not be internet-reachable now.
$ nc -vz TARGET 3945Seen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.