CallStop is a 100% effective robocall blocker — and it can protect any phone number.

CallStop is now available on the App Store

Maybe it’s 10PM and you’re settling down after a long day. Suddenly, your phone rings by your bed. It’s not a number you recognize, but it’s from your area code. It might be a friend you haven’t chatted with in a while, so you pick it up.

Big mistake. It’s a call from someone pretending to be from the IRS. They’re threatening to come after you for taxes you don’t owe. You quickly tell them to f*** off, or if you’ve been the more polite type, you say “Take me off of your list” like I was taught when I was young. But by picking up the phone, you’ve already made your first mistake. They now know you’re a great target for future scams — because you’re listening.

Hang on, though. What list were you asking them to take you off of? Maybe you meant the “Do Not Call List”, a federal registry is the United States. You do some digging and find this on the FCC website.

“Even if your number is registered, some organizations may still call you, such as charities, political organizations, and telephone surveyors. For a full description of who may still call you, please consult our Consumer FAQs. “

You realize the “Do Not Call List” doesn’t even work. A phone call about a political organization at any time of day feels like spam to you. It doesn’t matter whether they’re selling paper or political agendas — it‘s spam to you.

The federal list does nothing to block calls from an engineering standpoint: instead, it trusts that scammers and spammers won’t call those numbers out of fear of a fine or litigation. It’s too easy for spammers and scammers to switch numbers and create fake Caller IDs. Moreover, it’s so easy to hide behind spoofed or foreign numbers, the spammers couldn’t care less about a list that relies on trust. Most of these calls are from shady foreign numbers or numbers with no Caller ID. Good luck tracking down that person from a number in Liberia or Ukraine… chances are, they don’t even live there.

What would have happened if you hadn’t picked up the phone? Those scammers might have called you again at a different time of night. As you lay awake unable to sleep, infuriated by another obnoxious phone call, you realize you have to solve this problem to keep from going crazy.

You talk to your friends the next day and they mention a few apps that block spammy numbers. But they also tell you that those apps let calls through that haven’t yet been marked as spam. You tell them that’s not what you’re asking for — you want something that can block 100% of spam calls.

What you really need is an app that:

  1. Lets calls from contacts through seamlessly
  2. Allows an easy way for people to request to be on your whitelist (like Facebook friend requesting for phone numbers)
  3. Allows people with PINs to reach you by entering a PIN from a list you manage (you can put this in your email footer, for example)

3. Blocks everyone else

You’ve just described CallStop. CallStop is like Adblock but for phone calls.

My Story

To build CallStop, I needed a way to whitelist friends and family easily.

A few months back I was hanging out with my parents when we got a call. I only had a few minutes to chat with my dad before I had to hit the road. The call was a robocall — one of those tax scams. My dad listened for a few seconds, realized the call was a waste of time and hung up the phone. We completely lost our train of thought in the conversation we were having. So much for quality family time, for reasons out of everyone’s control.

But it did get me thinking: was there a way to solve this problem for myself? As an engineer and entrepreneur with experience building mobile apps and websites for startups, I wondered if the problem could be solved. I started doing research, and the results shocked me. I learned it costs 1¢ to make a robocall, and a single robocall center can make up to 16 million calls a day from purchased listed of hundreds of millions of numbers. The economics are totally broken.

I spent some time looking into existing solutions. T-mobile had a spam blocking app I found like many others on the App Store. But it could only find spam numbers after they were already spammy, which wasn’t what I was looking for. I wanted to be certain I wasn’t going to be called in the first place.

I realized how bad existing solutions were when I came across this contradictory suggestion by T-mobile. The carrier suggests changing your number if you keep getting unwanted calls! In my mind that’s giving up — and I like to think I’m not a quitter. No one is going to make me change my phone number, and no one is going to call me if I don’t want them to.

But that product didn’t exist when I looked for it, so I would need to build my own.

1’s & 0’s Don’t Cut It

I realized the problem with existing solutions is they’re all binary. These products have assumed numbers are either ‘spam’ or not, but the real world isn’t like that at all. You might want to only allow a business to reach you during business hours and prevent calls from coworkers on the weekend. You might want to restrict your pesky internet provider from bothering you by restricting the number of times they can call you in a month (that should teach them to tell you only the most important updates!). You might also want to prevent a delivery driver from texting you the night after they dropped off food by only allowing them to reach you before dropping off your food.

Building CallStop

Whilte burning the midnight oil, I prototyped the first version of CallStop. In those early days I was free to let my imagination roam. Most of all, I wanted to build a product that would solve the problem for everyone I knew. I came up with the name CallStop and got to work.

Goodbye, Spam Calls

Here’s what I came up with.

CallStop automatically imports your contacts into a whitelist and forwards your device number to your CallStop number. Unknown callers will hear the following message when they call your number:

You have reached a phone number protected by CallStop. If you know this person, press 1 to send a whitelist request with a quick note. If you have a PIN to reach this person directly, press 2 and enter the PIN.

Unknown callers hear this customizable message when calling you.

Listen to that recording here. It’s professional, succinct and guides callers clearly.

If the caller presses 1, they receive a text where they can add a note to their whitelist request. The person with the CallStop app gets a push notification, and when they open the app they see a note. It’s an effortless way to let new people reach you, but only when you want to be reached. Unknown callers can only send one whitelist request; they have to wait until you decide whether you want to respond and whitelist them. You’re in control.

The rejected calls section shows a list, updated instantly, of all callers that have heard your message. You can even call them back directly from that page. You can also optionally receive push notifications for rejected calls so you know instantly when you’re rejecting a call.

Customizing Your Voice Message

You can customize your voice message by recording a short, customized snippet similar to the one above. It makes your voice message slightly more personal. You can always update it or switch back to using the default voice message at any time.

Oh, and at any time if you’d like to let all calls through, just toggle “Accept All Calls” under the Settings section of your app.

CallStop takes less than 1 minute to set up, but protects against 100% of spam calls forever.

Does the app sound too good to be true? It’s not… it was a lot of work to build. Many late nights, stress and a ton of caffeine went into this product. But since I was solving the problem for myself and people I knew, I had a lot of motivation. Now, I need your feedback and ideas on how to make it better. My hope is the app can become the Adblock for phone calls, allowing people like myself to have full control over their phones.

CallStop Is Currently Free

CallStop is currently free. It’s a way to thank anyone who is an early user or anyone who finds this post. I need to learn more about how to improve the product, and for that I need users. I need to talk to people about what features they want, and how they use the product. It’s exactly what I love about working on startups: you get to meet interesting people and help them.

If this sounds like it solves a problem for you, try out the app here. It will save you a world of trouble. If you have any feedback, say hello to me at

I no longer get any spam calls, and can confirm I am much happier because of it. There’s a certain peace of mind of knowing I’ll never be bothered by spam callers. I know that every call I receive is someone who actually knows me.

Yesterday, I received 12 spam calls. Totally I installed CallStop, and I’ll never get any more ever again.

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Block 100% of spam and robocalls with CallStop. Learn more at

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Block 100% of spam and robocalls with CallStop. Learn more at

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