Why I built an expense tracker that literally cannot connect to the internet

likhith — Sun, 18 Oct 2026 04:19:08 +0000

Every modern finance app wants your data. They ask for your SMS permissions, link to your bank accounts via Account Aggregators, or scrape your emails. They promise to "keep it secure" on their servers.

I didn't want that for my own finances. So I built CashBuddy—an Android expense tracker that auto-captures your UPI transactions without ever asking for your identity, your SMS, or your internet connection.

Here is the technical reality of how it works, and why I made the trade-offs I did.

The Problem with SMS Parsers
Historically, Indian expense trackers read your bank SMS to log transactions. Google has rightly started cracking down on this. READ_SMS is a massive security risk. If an app can read your OTPs, it can drain your bank account.

So, I had to find another way.

The Solution: Notification Listening (On-Device)
Instead of reading SMS, CashBuddy uses Android’s NotificationListenerService. When you get a push notification from GPay, PhonePe, Paytm, or your bank app, CashBuddy intercepts it locally.

Here is the key part: The parsing happens entirely on your phone.
The app doesn't just read the notification; it runs a local extraction engine to pull out the amount, merchant, and timestamp. Once logged, the data is encrypted using AES-256, with the encryption key stored in the Android Keystore.

The "No Internet" Permission
If you check the AndroidManifest.xml in the GitHub repo, you will notice something missing:

It's not there. CashBuddy literally cannot send your data to a server. It doesn't have the permission to do so. You can put your phone in airplane mode and the app will function exactly the same.

The Hard Part: Friction and Custom Math
Building a privacy-first app means you can't rely on cloud AI to categorize things. I had to build the rules engine locally. Users can define custom formulas, set up merchant rules, and project their savings—all evaluated on-device.

What's Next?
CashBuddy is currently in closed testing on Google Play (I need to hit Google's 12-tester requirement to launch publicly). It's also open source.

Source Code: https://github.com/l1khith/CashBuddy

Google Group (for testers): https://groups.google.com/g/cashbuddy-alpha-testers

Opt-in Link: https://play.google.com/apps/testing/com.cashbuddy

If you are an Android user who cares about where your financial data lives, I'd love for you to test it. If you're a developer, I'd love your feedback on the notification parsing logic.

No servers. No tracking. Just math on your phone.

DEV Community: likhith

Why I built an expense tracker that literally cannot connect to the internet