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Fix Check Alive docs

docs/user-guide/check-alive.md

@@ -7,25 +7,31 @@
 
 ## What it does
 
-Check Alive defines a period of inactivity. When you open Electrum and more than that period has passed since the last postponement, the plugin asks whether you want to **push your delivery date further out** — because you are evidently still alive.
+Check Alive is a **warning threshold placed before your delivery date**. While the threshold is still in the future, nothing special happens: ordinary changes just refresh the will, anticipated by one day. Once the threshold has passed, the plugin tells you that the Check Alive threshold has passed and that you have to **invalidate your old will**, so that the delivery date can be pushed out — because you are evidently still alive.
+
+The check runs when you **close** the wallet, not when you open it.
 
 ![Check Alive parameter](../img/settings-check-alive.png){ .screenshot }
 *The threshold can be expressed as a relative period or an absolute date.*
 
 ## Example
 
-You set a delivery date **2 years** out, with Check Alive at **6 months**.
+You set a delivery date **2 years** out, with Check Alive at **6 months**. The threshold is therefore the delivery date minus 6 months: month 18.
 
 | What you do | What happens |
 |---|---|
-| You open Electrum after 3 months | Nothing — you are inside the Check Alive window |
+| You close Electrum at month 3, 9 or 15 | Nothing special — the threshold is still ahead. If something changed, the will is refreshed and anticipated by one day |
-| You open Electrum after 7 months | The plugin points out that your delivery date is now only 1 year and 5 months away, and offers to postpone it |
+| You close Electrum at month 19 | The threshold has passed: the plugin asks you to **invalidate your old will** and sign a new one with a later date |
-| You stop opening Electrum altogether | Nothing postpones the will. On the delivery date, the Will-Executors broadcast it |
+| You stop using Electrum altogether | Nothing postpones the will. On the delivery date, the Will-Executors broadcast it |
 
-As long as you keep using Electrum within the Check Alive window and accept the prompts, your will is never executed.
+If you accept the prompt when it comes, the will is pushed out and never executed. If you stop, the last date stands.
 
-!!! tip "Disabling it for a quick test"
+## Calendar reminders
-    Setting Check Alive to a **date in the past** effectively switches it off. This is what you want when testing the plugin with a delivery time only a few hours away, so the prompt doesn't get in the way.
+
+In advanced mode the plugin can export **`.ics` calendar reminders** spread across the Check Alive window (3 by default). The last one falls the day before the delivery date, so you are reminded before it is too late.
+
+!!! warning "A date in the past does not switch it off"
+    In advanced mode, a Check Alive **date in the past** counts as a threshold that has already passed: the plugin asks you to invalidate your will straight away. To test the plugin with a delivery time only a few hours away, use **basic mode** instead: there Check Alive is hidden and inactive, and never forces a postponement.
 
 !!! warning "Postponing is not free"
-    Accepting a postponement may require invalidating the previously committed transaction on-chain, which costs a miner fee. See [Postponing vs anticipating](updating.md#postponing-vs-anticipating).
+    Invalidating the previously committed transaction is an on-chain transaction and costs a miner fee. See [Postponing vs anticipating](updating.md#postponing-vs-anticipating).