The Ethereum Alarm service is a contract on the ethereum network that facilitates scheduling of function calls for a specified block in the future. It is designed to require zero trust between any of the users of the service, as well as providing no special access to any party (including the author of the service)

Scheduling Function Calls

Contracts, or individuals can schedule a function calls with the Alarm service by doing the following.

  1. Schedule the function call with the service, providing basic information such as what function to call and when it should be called.
  2. Register any call data that will be required to make the function call (optional for functions that have no arguments).

Call Scheduling

Function calls can be scheduled for any block at least 305 blocks (~75 minutes) in the future. Scheduling is done by providing the Alarm service with the following information:

  1. Contract address the call should be executed on.
  2. ABI signature of the function that should be called.
  3. Target block number that the call should be executed on.

Optionally, these additional pieces of information can be supplied.

  • Suggested gas amount that should be provided to the function. default: 0 to indicate no suggestion
  • Number of blocks after the target block during which it still ok to execute the call. (between 64 - 255 blocks) default: 255
  • Payment amount in wei that will be paid to the executor of the call. default: 1 ether
  • Fee amount in wei that will be paid to the creator of the Alarm service. default: 100 finey

The scheduling transaction must also include enough ether to pay for the gas costs of the call as well as the payment and fee values.

Once scheduled, the call waits to be picked up and executed at the desired block.

Registering Call Data

The Alarm service is not aware of the function ABI for the calls it executes. Instead, it uses the function ABI signature and raw call data to execute the function call.

To do this, any data that needs to be used in the call must be registered prior to scheduling the call.


Functions which do not have any arguments can skip this step.

Execution of scheduled calls

Scheduled function calls can be executed by anyone who wishes to initiate the transaction. Each call has a payment amount associated with it which is paid to the executor of the call.


In addition to the gas costs, schedulers are also encouraged to pay the call executor as well as the creator of the service for their effort. This value can be specified by the scheduler, meaning that you may choose to offer any amount for the execution of your function..

The scheduling function uses the following defaults if specific values are not provided.

  • Payment to the executor: 1 ether
  • Payment to the service creator: 100 finney


Will the call happen?

There are no guarantees that your function will be called. This is not a shortcoming of the service, but rather a fundamental limitation of the ethereum network. Nobody is capable of forcing a transaction to be included in a specific block.

The Alarm service has been designed such that it should become more reliable as more people use it.

However, it is entirely possible that certain calls will be missed due to unforseen circumstances. Providing a higher Payment amount is a potential way to get your scheduled call handled at a higher priority as it will be more profitable to execute.

Will I get paid for executing a call?

If you are diligent about how you go about executing scheduled calls then executing scheduled calls is guaranteed to be profitable. See the section on executing calls for more information.