Keys are acquired by hacking portals. It is not a guarantee you will get one on a hack, but it isn't really random either. If you already have the key the portal will not give another if it is in your inventory. there are ways around that. Like dropping the key for the portal and then hacking the portal then picking the key you dropped back up. or the use of capsules.
The first resonator you put on a Portal is worth 625AP. Plus it claims the portal as yours. I have notice some players just run around or drive by claiming of portals just to get the 625AP and their name. Then the move on. Especially if all they want is to get the credit toward unique portal captures to get there next badge and / or level (past level .
Yeah, me and the girlfriend running around hacking and linking on our way to the grocery store. Last night I walked that area doing the same thing, I think I hit close to 3 miles walking just last night.
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