Apple iMac (21.5-inch and 27-inch, Mid 2011) - Manual (Page 30)

30 Chapter 2 Life with Your iMac
Using the Apple Magic Mouse
Your Apple Magic Mouse, which comes with two AA batteries installed, is already
paired with your iMac. Pairing means your Apple Magic Mouse and iMac are connected
wirelessly and can communicate with each other.
About the Indicator Light
When you first turn on your Apple Magic Mouse, the light glows steadily for 5 seconds,
indicating the batteries are good. If you turn your mouse on and the indicator light
doesn’t glow, you may need to replace the batteries. See “Replacing the Batteries” on
page 56.
Indicator light
On/off switch