The Hidden Secret Code You Dial to Test If Your Calls Are Being Forwarded
I lost an evening to this code. A video told me that dialing *#21# would reveal whether my phone had been hacked, so I dialed it, and a screen came up listing an unfamiliar number next to the word "Voice." I spent the next three hours convinced someone was intercepting my calls: changing passwords, reading forum threads at midnight, seriously considering driving to a phone shop the next morning.
The number was my carrier's voicemail. It had been there since the day I got the SIM, because that's how voicemail works: unanswered calls get forwarded to a voicemail server, and that server has a number.
The code is real and genuinely useful. What it does is not what the internet says it does, and the gap between those two things is worth ten seconds of your time: because there is a real scam in this area, and it doesn't look anything like the viral version.
What the code actually checks
*#21# is an MMI code: a short string your phone passes to your carrier's network rather than processing itself. It asks one specific question: is call forwarding currently switched on for this line, and if so, where to?
That's it. It's a settings query about a carrier feature, answered by the carrier. Fact-checkers have repeatedly addressed the viral claim, and the answer is consistent: this code cannot detect spyware, monitoring apps, or a tapped line. Those operate on your device or elsewhere entirely and have nothing to do with call forwarding settings.
It's still worth knowing, for two honest reasons. It shows you forwarding you didn't set, which is the mechanism behind a real fraud, and it explains why calls sometimes aren't reaching you.
Fair warning before you try it: these codes are GSM standard, so they work on most networks and phones but not all. Some carriers, some Wi-Fi calling setups, and some regions return nothing or an error. That's normal and it isn't a sign of anything.
Step 1: Dial *#21# and read the whole screen
Open your dialer, type *#21# and press call. A response comes back within a second or two, listing services, Voice, Data, Fax, SMS, each marked as forwarded or not. "Not forwarded" across the board means unconditional forwarding is off. If Voice shows a number, note it down rather than panicking, because the next step is working out whose number it is.
Step 2: Check the conditional codes too
Try *#62# for forwarding when unreachable, *#67# for when busy, and *#61# for when unanswered. *#21# only covers unconditional forwarding, calls diverted before your phone ever rings, and it's genuinely normal for that to be off while the conditional ones point somewhere. These three are where your voicemail routing usually lives, which is exactly why most people see numbers here and immediately assume the worst.
Step 3: Identify the number before you do anything
Search the number you found along with your carrier's name. Nine times out of ten it's a published voicemail access number and you'll have your answer in fifteen seconds. If nothing comes up, ring your carrier, not a number from a search result, the one printed on your bill, and ask them what forwarding is configured on your line and when it was set. They can see it from their side, and it's a completely ordinary question for them.
My Expert Tip: The one genuinely worth watching is *#62#, forwarding when unreachable, pointed at a number nobody can identify. That's the setup used in a real attack: a fraudster configures conditional forwarding, then floods or busies your line, and calls you never see (including a bank's verification call) route silently to them while your phone sits there looking completely normal. Unconditional forwarding is obvious because you stop getting calls at all; conditional forwarding is invisible by design, which is exactly why it's the one that gets abused. And know before you clean up: ##002# clears all forwarding rules at once, including the ones sending calls to your voicemail, so voicemail can stop working afterward and you may need your carrier to switch it back on. Useful button, worth understanding before you press it.
Step 4: Turn off anything you didn't set
Use ##002# to cancel all forwarding, or go into your phone's call forwarding settings and switch off individual rules. On an iPhone that's Settings, then Apps or Phone, then Call Forwarding; on Android it's inside the dialer's settings. The menu route is gentler than the code because you can see and remove one rule at a time. Re-check with *#21# and *#62# afterward to confirm it took.
Step 5: Know what this doesn't tell you
If you're actually worried about your phone's security, this code is not the tool. It says nothing about monitoring apps, account access, or a compromised login. The things that do help: update the operating system, review which apps have permissions you didn't grant, check the list of devices signed into your main accounts, turn on two-factor authentication using an app rather than SMS, and change passwords from a device you trust. If you believe someone with physical access has installed something, a factory reset and a fresh restore is the reliable answer.
Step 6: Never dial a code someone gives you over the phone
If a caller claiming to be from your bank, your carrier, or tech support asks you to dial a string of symbols, hang up. The same family of codes that checks forwarding can also set it: one string queries, a very similar one redirects your calls to a stranger. Scammers use exactly this, because they only need your incoming verification calls, not your phone. On the same theme, treat a sudden unexplained loss of signal as worth a call to your carrier from another phone, since that's what a SIM swap looks like from your end.
What ten seconds is actually worth
The check itself takes about ten seconds and will, for the overwhelming majority of people, show voicemail routing and nothing else. That's a fine result: it's information, and now you know what your line looks like when it's normal.
The real value is the correction. I spent an evening frightened by a screen I'd misread, because a video told me something confident and wrong, and I suspect a lot of people have had that exact night. Knowing what a tool measures is worth more than knowing the tool exists.
And the genuinely useful part is the last step. The scam in this space isn't a mysterious code revealing a hacker: it's a friendly voice asking you to dial something. That one's worth remembering.
Dial *#21# now and see what your own line says: then hit the share buttons below and send this to whoever sent you that "check if you're hacked" video, because they deserve the real version.
