Using Ethereum's Alarm Clock for Scheduling Future Transactions

The Ethereum cryptocurrency-to-invest-in="">-to-invest-in/">blockchain allows for smart contracts that can execute transactions automatically based on certain conditions. One useful application of this functionality is the Ethereum Alarm Clock, which enables users to schedule Ethereum transactions to run at specific times in the future. The Alarm Clock utilizes the block timestamp to trigger transactions after a set number of blocks have been mined. This provides a decentralized "cron job" service for scheduling deferred Ethereum transactions.

How Does the Ethereum Alarm Clock Work?

The Ethereum Alarm Clock is comprised of two smart contracts that work together to schedule future transactions. When a user wants to set up a deferred transaction, they first call the Scheduler contract with details about the future transaction. This includes information like:

• Recipient address
• Value/amount to send
• Data payload
• Gas price
• Gas limit
• Block number to execute

The Scheduler records this information and creates a unique ID for the scheduled transaction. It then tells the user to make a payment to the Scheduler contract, which acts as a deposit to incentivize miners to execute the scheduled transaction.

Once the payment is made, the transaction is scheduled. The Scheduler contract communicates with a Library contract that keeps track of the queued transactions and their details. When the target block number is reached, the Library calls the Scheduler to execute the transaction as specified. The Scheduler then releases the deposited payment to the miner who mined the target block as a reward for executing the scheduled transaction.

Key Benefits of Scheduling Ethereum Transactions

There are several notable benefits to using the Ethereum Alarm Clock for deferring transactions:

• Set and forget - Once a deferred transaction is scheduled through the Alarm Clock contracts, everything happens automatically at the predetermined block number. Users don't have to remember to manually send a transaction later.
• Gas price flexibility - Gas prices fluctuate frequently on Ethereum. With the Alarm Clock, users can set a gas price that makes sense for when the transaction is scheduled, rather than paying today's price.
• Security - Scheduling future transactions through the Alarm Clock's smart contracts provides security benefits compared to external scheduler services. Payments are held in the contract until the transaction is executed as promised.
• Reliability - As long as there are miners securing the Ethereum blockchain, transactions scheduled via the Alarm Clock will execute reliably at the specified block number. There is no centralized service outage risk.

Use Cases for Scheduling Ethereum Transactions

There are many potential uses of the Ethereum Alarm Clock for scheduling future transactions. Here are some examples:

Recurring payments

The Alarm Clock could be used to set up recurring Ethereum payments at set intervals by scheduling a series of transactions with increasing block number targets. This could act like a subscription service billed monthly/yearly etc.

Future contract settlements

Financial contracts with future settlement dates could automatically execute via the Alarm Clock. For example, options or futures contracts could pay out at expiration by scheduling a transaction to transfer funds at a specific block number.

Birthday money transfers

You could use the Alarm Clock to setup anniversary payments by scheduling a gift transfer to a loved one annually on their birthday.

Token vesting schedules

Token creators can use the Alarm Clock to distribute vested token grants on a set schedule, automating the unlocking of tranches at specified blocks.

Auctions & bids

Auctions ending at a set block number could automatically finalize bidding and transfer funds to the winner at the expiration block via a scheduled transaction.

Scheduling Transactions Far in the Future

One challenge with the Ethereum Alarm Clock is that transactions can only be scheduled a certain number of blocks in the future. This is because the Ethereum blockchain has a limited window of mineable blocks before the difficulty bomb induces a hard fork (The Bombsection of the design rationale for this).

However, there are a couple ways to schedule transactions very far in the future, like months or years later:

• Relayers - A network of relayers could continually reschedule pending transactions so they remain active on the Alarm Clock contracts. Someone would need to manage this rescheduling process over time.
• Long-running Oracle - An Oracle contract that stays active indefinitely could be used to watch the block number and re-queue transactions on the Alarm Clock when the initial schedule expires.

Neither method is perfect, but they allow for extending the scheduling window considerably. The devs could also simply delay or remove the difficulty bomb to expand the block space available. But that requires a hard fork change.

Is the Ethereum Alarm Clock Reliable?

I created the Ethereum Alarm Clock contracts back in 2018 to explore this concept of scheduling future transactions. It works reliably via some clever incentive mechanisms in the contract design. Miners are compensated for executing deferred transactions, so the incentive structure ensures transactions are executed on time.

However, the Alarm Clock is still considered alpha software. As usage and values increase, we might find incentives are inadequate or other issues arise. Like all decentralized software, rigorous testing and iterating on the contract design will be key to making the Alarm Clock production-ready.

But the core premise is sound. By utilizing Ethereum's block timestamp and smart contract capabilities, we can build "trustless" cron jobs. I'm excited to see this primitive mature and become an integral part of the Ethereum developer toolkit.

How Long Until ETH 2.0 Makes Alarm Clock Obsolete?

Once Ethereum moves to proof-of-stake consensus with ETH 2.0, the threat of the difficulty bomb inducing hard forks will disappear. This should allow scheduling transactions arbitrarily far in the future. At that point, the Ethereum Alarm Clock may no longer be necessary.

However, the Alarm Clock provides other benefits beyond just long-term scheduling. Its smart contracts offer reliability, security and incentive mechanisms that may still prove useful in an ETH 2.0 world. But only time will tell if developer needs are met natively by new protocols or if purpose-built tools like the Alarm Clock remain relevant.

Either way, the Alarm Clock will likely have served its purpose in pushing forward innovation and providing a valuable service during Ethereum's proof-of-work era. The core capability it unlocked—scheduling future transactions based on block timestamps—will persist and evolve to meet needs on ETH 2.0 and beyond.

Conclusion

The Ethereum Alarm Clock demonstrates the unique capabilities of smart contract platforms. By encoding transaction logic and scheduling directly on the blockchain, decentralized cron jobs are possible without relying on external services. This expands the potential for automatic, delayed execution of transactions in DeFi, recurring payments, scheduled actions and more.

As Ethereum scales and matures, expect to see the functionality of tools like the Alarm Clock incorporated into core protocol layers and developer frameworks. The need for time-based transaction scheduling isn't going away. And the Alarm Clock has sounded as an early harbinger of this on-chain future being built before our eyes.