Watchtowers

A watchtower monitors the blockchain for revoked commitment broadcasts on your behalf and can publish justice transactions if you are offline.

Why this matters

Phones sleep. Laptops close. Lightning’s penalty model needs someone watching. Towers extend security to intermittent devices.

Analogy

A neighborhood security camera that only unlocks the evidence locker if a specific break-in pattern appears, and it does so without learning your daily life.

Worked mental model

Re-read the diagrams in this lesson once out loud in plain language. If you cannot explain the flow to a friend without jargon, pause and revisit Mastering Bitcoin / Mastering Lightning chapters linked in Resources. Chapter references are intentional, not decorative.

Hands-on habit

Every protocol idea should be paired with one local experiment:

1. Reproduce the happy path on regtest (or Polar for Lightning)
2. Break it on purpose (wrong fee, expired invoice, offline peer)
3. Write down what error you saw and which layer produced it (wallet, node, mempool, peer)

That habit turns reading into builder instinct.

Glossary check

Pick three terms from this lesson and define them in one sentence each without opening notes. Weak definitions mean the lesson is not finished yet.

Resource order

Use Resources in order: narrative book chapter first, then BIP/BOLT for precision, then implementation docs for commands. Jumping straight to RPC flags without the mental model creates brittle knowledge.

Next steps

Build a Lightning POS: invoices, webhooks, and settlement UX.