Lightning channels close cooperatively or by force. Watchtowers watch the blockchain and punish cheating while you are offline. Learn how closing works.
Two ways to close
| Cooperative close | Force close | |
|---|---|---|
| How | Both sign a final transaction together | One side broadcasts its latest commitment |
| Speed | Funds available after confirmation | The closer waits a CSV delay (often 1–2 weeks) |
| Fees | Low, negotiated | Higher, pre-agreed |
| When | Normal case | The peer is offline or unresponsive |
The cheating problem
Every old commitment is still a validly signed transaction. A cheater could broadcast an old one where they had more money. The protection: their own funds in that transaction are timelocked, and the honest party holds a revocation key for it.
If you spot an old state on-chain during the delay, you broadcast a justice transaction and take the entire channel balance.
Watchtowers
That only works if someone is watching. A watchtower is a service you give encrypted breach data. It can't see your channels, but if it sees a matching old commitment on-chain, it broadcasts the justice transaction for you.
Practical tips
- Keep your node online, or use a watchtower.
- Back up channel state with the method your software recommends (static channel backups).
- Prefer cooperative closes; force closes cost more and take longer.
Static channel backups
A static channel backup (SCB) can't restore channel balances, but it lets you ask your peers to force-close so your funds return on-chain. Keep an up-to-date copy whenever you open a new channel.
Spot a force close on-chain
A force-close transaction spends the channel's funding output into outputs with timelocked scripts. After the delay, a second transaction sweeps the funds to the owner's wallet.
Key takeaways
- Cooperative closes are cheap and fast; force closes wait on a timelock.
- Broadcasting an old state lets the other side claim everything.
- Watchtowers watch the chain for you while you're offline.
Common questions
What happens to in-flight payments in a force close?
Pending HTLCs are resolved on-chain by revealing the secret or waiting for the timeout.
Do watchtowers learn my balance?
Standard designs give them encrypted data they can only decrypt if a breach actually occurs.
How long does a force close take?
The closing transaction confirms like any other; the closer's own funds then wait for the agreed delay, often around one to two weeks.
Do I need a watchtower?
If your node may be offline for longer than the channel's delay, yes.