Unknown number lookup — free scam-number checker
Paste any phone number — landline, mobile, international, short code — and we'll check it against the GACS public blacklist of reported scam numbers plus global sanctions sources in under 2 seconds. No app to download, no account to create, no upsell.
Check an unknown number
Works with any format — +1 415 555 0188, (415) 555-0188, 4155550188. International numbers welcome (include the country code with a + prefix).
No account, no email, no contact-list upload. Reports identified only by a local browser fingerprint.
3 unique reports auto-promote a number to the live blacklist. Public, auditable, search-engine indexed.
US, UK, EU, Australia, Canada, India and beyond. Works for landlines, mobiles, and SMS short codes.
What to do when an unknown number contacts you
1. Don't pick up — let it go to voicemail
Legitimate callers leave a message. Robocallers and live scammers usually don't — they don't want a recording on record. Saying "hello" or pressing any key confirms a live human and moves your number up the autodialer priority list.
2. Look the number up before you call back
Use the tool above. Then Google the full number in quotes. If it claims to be your bank, hang up and call the number printed on the back of your card — never call back the number that contacted you. This single rule blocks almost every phone-based fraud.
3. Never share codes, OTPs, or payment details by phone
No real bank, no real tax office, no real delivery company will ever ask you to read out a verification code. The moment they do, you are talking to a scammer. Hang up.
4. Report what looked off
One click after the lookup adds the number to the public GACS registry. Your report protects every person who looks up that number after you.
Where to report scam numbers in your country
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United States
Report scam calls to the FTC at donotcall.gov/report. The FCC also runs reportfraud.ftc.gov. Carrier: dial #662# on T-Mobile / Metro for free call-blocking.
United Kingdom
Forward scam texts to 7726 (free, all UK carriers). Report scam calls to Action Fraud (actionfraud.police.uk). Ofcom monitors CLI-spoofing complaints at ofcom.org.uk/complaints.
Australia
Report to Scamwatch (scamwatch.gov.au). Forward scam SMS to 0429 999 888 (ACMA). Add your number to the Do Not Call Register (donotcall.gov.au).
Canada
Report to the Canadian Anti-Fraud Centre at antifraudcentre.ca or 1-888-495-8501. CRTC handles unwanted-call complaints at lnnte-dncl.gc.ca.
India
Report cybercrime at cybercrime.gov.in or call 1930. Forward scam SMS by reporting to your operator's UCC (Unsolicited Commercial Communication) shortcode.
Germany / EU
Report to the Bundesnetzagentur (bundesnetzagentur.de) for spam/scam calls. Across the EU, your national telecoms regulator handles CLI-spoofing complaints.
Unknown number lookup — frequent questions
Is GACS unknown number lookup really free?
Yes. No signup, no email collection, no upsell. We check the number against the GACS public blacklist of reported scam numbers, plus global sanctions sources. The full lookup is free for every visitor, every time.
Where does the scam-number data come from?
GACS aggregates three sources: (1) public reports submitted directly to GACS by visitors and verified, (2) global sanctions and sanctioned-entity registries (OpenSanctions), and (3) cross-checks against scam-number lists republished from law-enforcement portals where licence permits. When 3 unique people report the same number, it auto-promotes to the live blacklist.
What if the number doesn't show up in the database?
Most scam numbers rotate every few days, so a clean lookup doesn't guarantee safety. Apply the universal rules: don't share codes, don't pay over the phone, don't click links in unsolicited texts, and call back the company on a number you find on their official site — never the one in the message.
How do I find out who called me from an unknown number?
Three steps: (1) paste the number into the lookup tool above to see if anyone has flagged it as a scam, (2) Google the full number in quotes — legitimate businesses usually have it on their site, (3) if it claims to be your bank / Amazon / 'the IRS', hang up and call the official number from the company's website or the back of your card. Never call back the number from caller ID itself.
Should I call back an unknown number?
No. Returning a missed call from an unknown number can incur premium-rate charges (the 'Wangiri' scam — one-ring callback scams hit numbers worldwide). If it's important, the caller will leave a voicemail. If it's a delivery, the courier will text you a tracking link from a verified short code.
What's the difference between this and Truecaller?
Truecaller requires an app install, account creation, and uploads your entire contact list to their servers — which is how their database is built. GACS is the opposite: a free web lookup that needs nothing from you. We never see your contacts. Reports are anonymous, identified only by a randomly generated fingerprint stored locally in your browser.
Can I report a scam number anonymously?
Yes. After checking a number above, click 'Report as scam' — one click, no email, no signup. The report adds to the public count for that number. When 3 unique people report the same number it auto-promotes to the live blacklist and gets a dedicated warning page indexed by Google.
Related GACS tools
Lookup checks the GACS blacklist (crowdsourced reports), OpenSanctions, and republishable scam-number lists. Free for every visitor, every time. No data sold, no contact list uploaded. Last reviewed June 22, 2026.GACS does not provide reverse-name identification. We only tell you if a number is known to be a scam, not who owns it.