Pacer Cash

Making a simple mistake shouldn't cost you a fortune. When you accidentally send money to the wrong person with your credit card or fall victim to fraud, you can dispute the charge and get your money back. But in crypto? One wrong character in an address, and your funds are gone forever. This is one of the biggest barriers preventing mainstream adoption of crypto payments - the lack of safety nets.

That's why we built Pacer - a smart contract wallet that brings traditional financial safety mechanisms to crypto, without compromising on decentralization. At its core, Pacer implements a mandatory timelock on all transactions. Think of it like a built-in cooling-off period: when you make a transaction, it doesn't execute immediately. Instead, it's queued for 24 hours, giving you time to catch any mistakes or flag suspicious activity.

If something goes wrong, you can dispute the transaction through Kleros, a decentralized arbitration system. This works similarly to how you'd dispute a credit card charge, but instead of relying on a centralized authority, your case is reviewed by a decentralized court of jurors. You maintain the benefits of decentralization while gaining the security of traditional finance.

But we understand that sometimes you need immediate transactions. That's where our Halo chip integration comes in. It's like having a hardware key to your wallet - if you authenticate with your Halo chip, you can bypass the timelock entirely. This gives you the best of both worlds: security when you need it, speed when you want it.

What truly sets Pacer apart, though, is our ultrasound payment system. Imagine being able to make crypto payments without an internet connection. Using ultrasonic sound waves, we've made this possible. A merchant can generate a payment request, your phone emits an ultrasonic sound containing the signed transaction, and the merchant's device captures it. Once internet connectivity is available, the transaction is broadcast to the network. This is game-changing for regions with limited internet access - suddenly, cryptocurrency becomes as accessible as cash.

Under the hood, we're using Biconomy's Account Abstraction stack and their gasless transaction infrastructure, but we've implemented it headlessly to maintain full control over the user experience. Authentication is handled through Privy, again used headlessly, allowing users to log in with familiar methods like email or social accounts while maintaining self-custody of their funds.

What we've created isn't just another crypto wallet - it's a bridge between the security and familiarity of traditional finance and the innovation and freedom of crypto. By making crypto transactions safer, more accessible, and more practical for everyday use, we're addressing the real barriers that have kept mainstream users from embracing cryptocurrency. This is about making crypto work for everyone, not just the tech-savvy.

Think of Pacer as your safety net in the crypto world - all the benefits of decentralized finance, but with the safety features you've come to expect from traditional financial services. No more stress about irreversible mistakes, no more exclusion due to poor internet connectivity, just simple, secure, accessible crypto payments for everyone.

When we set out to build Pacer, we knew we wanted to create something that felt as familiar as traditional banking but maintained the core tenets of crypto - decentralization and self-custody. Here's how we pieced it all together.

The foundation of Pacer is built on Biconomy's Account Abstraction infrastructure, but we took an unconventional approach. Instead of using their standard UI components, we stripped everything down to its core and implemented their SDK headlessly. This gave us complete control over the user experience. The same approach was applied to Privy - we're only using their authentication and EOA management capabilities while building our own streamlined onboarding flow. This means users can log in with familiar methods like email or Google, but behind the scenes, they're getting true self-custodial wallets.

The heart of our security innovation is the timelock validator - a custom smart contract that serves as a mandatory module for all Biconomy smart accounts created through Pacer. Every transaction gets queued for 24 hours by default, creating a security window where suspicious activities can be disputed through Kleros Court. One particularly tricky part was ensuring that disabling the timelock itself requires a 24-hour waiting period - this prevents attackers from quickly disabling security features during a compromise attempt.

The integration with Halo chips was probably our hackiest achievement. We created a bridge between the physical chip's authentication and our smart contract validator. When a valid Halo signature is detected, it creates a bypass path in the validator contract, allowing trusted users to skip the timelock entirely. Getting this to work seamlessly while maintaining security was a significant challenge - we had to carefully balance convenience with security.

But I believe our most innovative technical achievement is the ultrasound payment system. We developed a protocol that uses ultrasonic sound waves for transaction signing, enabling completely offline crypto transactions. The technical challenges here were significant - we had to build custom error correction into the ultrasonic protocol to handle ambient noise and ensure reliable transmission. We're using specific frequency ranges that work across most smartphone speakers and microphones while remaining inaudible to humans.

The architecture looks like this: when a merchant initiates a transaction, they generate a QR code containing the transaction details. The customer's phone signs this transaction and converts the signed data into a series of ultrasonic pulses. The merchant's device captures these pulses, reconstructs the signed transaction, and queues it for broadcast when internet connectivity is available. This required careful consideration of data encoding, error correction, and acoustic channel characteristics.

We're using Biconomy's paymaster for gasless transactions, but we implemented our own batching logic to optimize gas costs for queued timelock transactions. This means users never need to worry about gas fees, making the experience much more like traditional finance.

All these components - the AA wallet, timelock validator, Kleros integration, Halo authentication, and ultrasound payments - are tied together behind a unified API layer. This modular approach means we can easily add new features or swap out components as better solutions become available.

The most challenging part was making all these pieces work together seamlessly, especially in offline scenarios. A user needs to be able to queue transactions, sign them ultrasonically, and have them automatically broadcast when internet connectivity is restored - all while maintaining the security guarantees of the timelock system and gasless operations.

This infrastructure opens up cryptocurrency to entirely new use cases and demographics. In regions with limited internet access, smartphones effectively become offline crypto point-of-sale devices. It's not just about making crypto more secure - it's about making it truly accessible to everyone.