Canon EOS M Instruction Manual page 17

Handling Precautions
If the camera has not been used for an extended period, test all its functions
before using it. If you have not used the camera for some time or if there is
an important shoot coming up, have the camera checked by your Canon
dealer or check the camera yourself and make sure it is working properly.
When you detach the lens, the image sensor will be exposed. To prevent
scratching the image sensor, do not touch the image sensor.
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