Just a heads up for those updating to the latest OS X 10.11.5 — it messed with the Bluetooth on my iMac (latest model). The trackpad and keyboard kept dropping the connection and then reconnecting. Only way to fix it was to delete the pairings and re-pair both. Oddly enough, my Magic Mouse (the new one) had a solid connection. If it's weird, I'll see it.
"I really need a new tagline"
—P M Evans