Show HN: FitVow – a smart contract that fines me if I miss weekly fitness goals

[the42thdoctor]

FitVow is my personal commitment-device experiment: I lock funds in a smart contract for 12 weeks, define weekly fitness goals, and if I miss a week a penalty becomes enforceable.

Enforcement is permissionless: anyone can call the contract and a portion of the penalty is paid to the caller; the rest goes to a charity (Giveth).

Weekly activity data comes from my smartwatch (via Samsung Health / Health Connect), synced by an Android app that publishes the weekly activity on-chain.

The site is mostly a viewer for on-chain state. Full write-up / architecture / security notes in the first comment.

[the42thdoctor]

Author here: I built this because I kept finding ways to “renegotiate with myself” on weeks I didn’t feel like training. I wanted a commitment device with real consequences and no trusted referee — just code and incentives.

Write-up / architecture / threat model:

https://pedrooaugusto.github.io/blog/posts/making-missed-wor...

Current run parameters:

- Network: Arbitrum (Ethereum L2)

- Duration: 12 weeks (Jan 19 → Apr 13)

- Total stake: ~$235 (0.075 ETH)

- Penalty per failed week: ~$19 (0.00625 ETH)

How enforcement works:

- If a week fails, anyone can call enforceAgreement() and receive a share of the penalty; the rest goes to the Giveth charity.

- There’s also a Chainlink Automation backstop so “nobody enforced” can’t become an escape hatch. If automation is the first to enforce a missed week, there’s no caller to reward, so 100% of the fine goes to Giveth.

I’d love feedback on:

1) where you’d try to cheat this,

2) what would make it more verifiable/auditable to you.