How Caller Display Works - And Why it's Not Always Secure

How Caller Display Works - And Why it's Not Caller display (caller ID) is something most of us take for granted. We see a number pop up and assume it accurately represents the caller. But is that assumption safe?

How Caller ID Works

Caller ID originated in the Public Switched Telephone Network (PSTN) and still underpins much of telephony today.

When a call is made, the caller ID information is set by the originating carrier or VoIP system, not verified by the receiving phone.

Historically, there was no universal verification, meaning the displayed number could be manipulated.

Why Caller ID Can Be Spoofed

Because the system relies on trust rather than cryptographic validation, attackers can spoof caller ID—making a call appear as if it's from any number they choose.

Spoofing is often used for scams, phishing, and fraud.

Modern Protections

New standards like STIR/SHAKEN (Secure Telephone Identity Revisited / Signature-based Handling of Asserted information using tokens) are being deployed in many regions.

These protocols cryptographically verify caller ID on IP-based networks, reducing spoofing—but adoption is incomplete, especially across international and legacy systems.

Hong Kong does not mandate STIR/SHAKEN for caller ID authentication.

Impact on Trust

Caller ID is not foolproof. It creates a false sense of security because most users assume the displayed number is authentic.

What You Can Do

Be sceptical of unexpected calls—even from familiar numbers.

Never share sensitive information unless you initiated the call.

Use call-blocking or spam-detection apps.

Verify important calls by hanging up and calling back through official channels.

The bottom line? Don't let a familiar number fool you. When it comes to caller ID, trust but verify.

What's your experience with suspicious calls? Let's discuss in the comments.Always Secure