Not sure what you mean by "sitting down." You can create location based Reminders in the Reminder app.
Add a location: Tap Location, then choose where you want to be reminded—for example, when you arrive home or get into a car with a Bluetooth connection to your Apple Watch.
Your Apple Watch notifies you of reminders you create in the Reminders app on your iPhone—and on other devices where you’re signed in to iCloud using your Apple Account.
Not sure what you mean by "sitting down." You can create location based Reminders in the Reminder app.
Add a location: Tap Location, then choose where you want to be reminded—for example, when you arrive home or get into a car with a Bluetooth connection to your Apple Watch.
Your Apple Watch notifies you of reminders you create in the Reminders app on your iPhone—and on other devices where you’re signed in to iCloud using your Apple Account.
Well, all I know is you can set reminders/alerts when you arrive/leave a location. I don't know of any way to set reminders when you are doing a particular activity.
I saw this post on Reddit, not sure what the sitting down has to do with it. But yes you can easily tell Siri to set a reminder when you arrive at a location.