An unknown number calls right when you’re expecting a delivery. Is it your Uber Eats driver, or just another junk call about a pre-approved loan you don’t want? Blocking that specific spammer feels pointless because they just call back from a different number some minutes later.
While my Galaxy S24 Ultra has built-in spam protection, I wanted more control over who gets through. That’s when I found SpamBlocker. It’s a free, open-source Android app packed with tons of filtering options, and it comes with one huge perk: I can block the junk without having to replace my favorite everyday phone and texting apps.
SpamBlocker gets the screening job, not the whole phone
Setup takes a few permissions and a little housekeeping
SpamBlocker is free and supports Android 10 and newer. Install it through F-Droid, the open-source app repository that recently had a welcome overhaul. If you’re installing outside Google Play, stick to the official listing or developer’s GitHub, since unofficial forks exist.
After you open it, the app shows three tabs: Call, SMS, and Settings. History records screening decisions, while Settings houses contact exceptions and rather fearsome-looking regular expressions. Most can wait.
To start screening calls on your phone:
- Open Settings > Apps > Choose default apps > Caller ID & spam app.
- Select SpamBlocker, then enable Call under its Screening settings.
- Grant Contacts access if you want contact-based rules to work, along with any other permissions needed for the features you enable.
My Samsung Phone app stayed in place for dialing and answering. SpamBlocker uses Android’s caller screening role, although selecting it may replace another service such as Truecaller in that particular role. Remember that if you’ve already fine-tuned Samsung’s spam-blocking settings.
Setting up text filtering is just as easy but requires a separate step. To filter texts, enable SMS filtering in SpamBlocker and grant the SMS and notification permissions it requests. SpamBlocker then handles incoming SMS alerts while your regular messaging app continues to receive and store messages. That means spam messages can still appear in your inbox, but they won’t keep interrupting you. To avoid double notifications for every text, turn off notifications in your regular messaging app.
If you use RCS in Google Messages, be careful about disabling all its notifications. SpamBlocker can’t handle RCS chats, so you could end up missing those alerts too. If your messaging app doesn’t offer separate notification controls for SMS and RCS, keeping its notifications enabled and putting up with duplicate SMS alerts may be the safer choice.
You get to write the rules
A blacklist with quite a good memory
Under Regex Settings, tap New next to Number Rules, then tap Customize. You can set a rule to match one exact number, the first few digits of a number (a prefix), or a pattern. Then choose whether the rule allows or blocks the call. You’ll also see a priority field, SIM selection, a notification level, and a schedule. If regular expressions make your eyes glaze over, just start with a single number.
The basic steps are pretty simple:
- Type in a number or pattern, and give the rule a name you’ll recognize.
- Select Call, choose Block, and set Block Type to Reject.
- Save your changes, then type a test number into the Rule Testing box to make sure it works before a real call comes in.
One common trap to watch out for is how numbers are formatted. A number saved in your contacts with an international code (like +1 for the US) might show up on a local call without it. If your rule looks for an exact match, it might miss the call entirely. Luckily, SpamBlocker has features like Raw Number and Ignore Country Code to handle this. Once you’ve adjusted the rule to cover both formats, try calling from a matching number to check whether SpamBlocker rejects it. The Call tab keeps a history of screening decisions, making it easier to see which rule was responsible.
Keep an eye on rule priority, too. For example, give your allow rules for friends and family a higher priority than general block rules so you don’t accidentally reject someone important. SpamBlocker checks higher-priority rules first, and a broad blacklist can cause trouble if it takes precedence over an exception.
Text filters look inside the message
Head over to Message Rules, tap New, and tap Customize to open up a text-filtering editor that works just like the call blocker. This time, you can type in specific words or phrases to look for, and even add a rule for specific senders. For example, entering a regular expression like (?i).*exclusive offer.* will catch that phrase no matter where it is in the text, without worrying about capital letters. You can test your rule with a fake text message first and check the app’s SMS history to see if it works before letting it loose on your everyday texts.
It knows when an unknown caller might matter
Exceptions save the day
The best spam filters leave a little breathing room for real-life emergencies. For instance, the Repeated Call feature lets a persistent caller get through if they call back within a certain timeframe—perfect for when a family member or friend is trying to reach you from an unknown number in an emergency. The feature also needs access to your call history, which you’ll have to grant separately. On the flip side, you can set a minimum wait time between those calls so an automated robocaller slamming the redial button doesn’t trick the system. You can even set it up to check for text message activity, too.
Another clever feature is called Recent Apps. If you turn it on and specify a timeframe, SpamBlocker can allow calls after you’ve recently used a particular app. Think about ordering food on DoorDash and receiving a call from an unfamiliar number a few minutes later. The catch is that SpamBlocker can’t tell whether that caller is actually your delivery driver. Any number could benefit from the exception during that window, so keep it reasonably short. The feature also requires Android’s Usage Statistics permission, which you have to grant manually.
The app also comes packed with extra tools like custom schedules, spam databases, online number lookups, and experimental AI-style text filtering. If you’re just starting out, it’s best to stick to the offline rules and expand slowly as you get comfortable. The developer’s privacy policy explains that online lookup services can see the phone numbers you query and certain connection details. The offline filters, meanwhile, can process numbers and messages locally without sending them to those services.
The spammers can keep trying their luck
SpamBlocker asks you to do a bit of thinking upfront, which is fair payment for the control it offers. Once the rules are sensible, your Phone app can carry on being a Phone app. Meanwhile, the unsolicited sales department can keep dialing into the void.
