OTP and two-factor authentication explained
The code you type is the simplest piece of security on the internet, and still the most common.
SMS Nitro team ·
What is an OTP?
An OTP (one-time password) is a short code valid for one login or action, delivered by SMS, email, voice or generated by an authenticator app. Two-factor authentication uses it as a second proof after the password. SMS OTPs are convenient but can be intercepted by SIM swap or phishing; authenticator apps and passkeys are stronger.
Types of second factor
- SMS or voice code: anything that receives at that number.
- TOTP app: time-based code generated on your device.
- Push: approve on a trusted device.
- Passkey or hardware key: cryptographic, phishing-resistant.
Temporary numbers and 2FA
Use a temporary number to pass sign-up verification, then move the second factor to an authenticator app. If the service only offers SMS 2FA, rent the number so it remains yours at the next login.
SMS Nitro at a glance
| Billing | Pay only if the code arrives. If no SMS arrives before the number expires, the frozen amount returns to your balance automatically, in full. |
|---|---|
| Number reserved for | Up to 20 minutes per activation. Rentals from 24 hours to 30 days with unlimited incoming SMS. |
| Payment | Card via Stripe (Visa, Mastercard, Amex, Apple Pay, Google Pay) or crypto (USDC or SOL on Solana). Minimum top-up $5. Card top-ups carry a 10% processing fee; crypto has none. |
| Subscription | None. Pay per verification; your balance never expires. |
| Countries | 180+ countries, including the United States, the United Kingdom, Canada, India, Germany, Brazil, Indonesia and the Philippines. |
| Apps | 700+ apps and websites: WhatsApp, Telegram, Google, Instagram, TikTok, Discord, OpenAI, PayPal, Tinder, Amazon and more. |
| Developers | REST API plus an SMS-Activate-compatible endpoint. API key available after your first top-up. No API surcharge. |
| Support | Tickets from the dashboard and email, answered by people. |
| Price | From $0.02 per verification code, depending on the app and the country. |
Frequently asked questions
Is SMS 2FA better than nothing?
Much better. It stops password-only attacks, which are the majority.
Is SMS 2FA safe enough?
Better than password only; weaker than an authenticator app or a passkey. Use the app where possible.
Can I use a temporary number as my 2FA number?
Only a rented one, kept renewed. A one-time number will not receive future codes.
What is a passkey?
A cryptographic login tied to your device, resistant to phishing. Many services now offer it instead of SMS.