How to detect disposable phone numbers in user sign-ups
This guide explains what disposable phone numbers are, why they are a serious problem for SaaS and online platforms, and how you can reliably detect them without hurting user experience.
What are disposable phone numbers?
Disposable (or temporary) phone numbers are phone numbers that can be rented or generated for a short period of time. They are widely available through online services and mobile apps, often for free or at very low cost.
These numbers are commonly used to:
- Receive SMS one-time passwords (OTP)
- Bypass sign-up restrictions
- Create multiple accounts on the same platform
Once the verification is completed, the number is often discarded and never used again.
Excerpt from a set of disposable numbers available for free on the website quackr.io
Why disposable phone numbers are a problem
At first glance, SMS verification seems like a strong defense. In practice, disposable numbers make it trivial to bypass.
Here is the real impact on your business:
1. Fake accounts at scale
Fraudsters can create hundreds or thousands of accounts automatically, polluting your user base and analytics. A March 2026 study estimated a fake account rate of 37.2% among a diverse panel of applications.
2. Abuse of free trials and promotions
Disposable numbers are heavily used to exploit free trials, referral bonuses, and discount codes. In 2020, PayPal’s sign-up incentives backfired when fraudsters used bots to create 4.5 million fake accounts. This massive bot attack forced a major cleanup and wiped out nearly a quarter of the company’s market value.
3. Increased SMS costs
Every OTP sent to a burner number costs you money — with zero chance of retaining a real user. Indeed, OTP messaging services such as Twilio charge $0.0083 per text message sent.
4. Lower trust and platform quality
Fake accounts lead to spam, scams, and poor user experience for legitimate users. Here is an example of a common use case for Tinder scams involving the creation of fake accounts.
How to detect disposable phone numbers
Reliable detection requires phone number intelligence, not just verification.
1. Identify known disposable number providers
Many temporary numbers come from well-known ranges used by SMS rental services. Maintaining and updating these ranges is critical.
2. Analyze number usage patterns
Disposable numbers often show abnormal behavior:
- Extremely short lifetime
- No reuse by real users
- High velocity of account creation
3. Check carrier and number type signals
Certain carriers and number types are statistically more likely to be disposable.
4. Use a dedicated detection API
Building and maintaining this logic internally is costly and error-prone. A specialized API can return a risk signal in real time.
Where to place detection in your sign-up flow
The best place to detect disposable numbers is before sending the OTP.
A common flow:
- User enters phone number
- Phone intelligence check (risk assessment)
- Decide to allow, block, or flag
- Send OTP only if risk is acceptable
This approach reduces SMS costs and stops abuse earlier.
How Rekonit helps
Rekonit provides a real-time API designed specifically to detect disposable and temporary phone numbers.
With Rekonit, you can:
- Detect disposable numbers before sending OTPs
- Integrate in minutes with a simple API call
- Ensure a 99.95%+ availability, designed for real-time API usage
- Benefit from a low-latency responses optimized for real-time user onboarding
- Monitor the evolution of fraud with a 24/7 proactive incident detection
The API is built for high availability and low latency, making it suitable for critical sign-up flows.
Final thoughts
Disposable phone numbers are no longer an edge case — they are one of the most common vectors for account abuse.
If your product relies on phone verification, adding phone number intelligence is no longer optional. Detecting disposable numbers early protects your platform, your users, and your growth.
Want to see how disposable number detection fits into your product? Get started with Rekonit and secure your sign-up flow in minutes.