New car question, please answer 2011 nissan sentra, with intellect key?

I just bought a new Nissan sentra 2011 last week, this morning i noticed when i had my front and back door on my left open, a red icon of a key started to blink on my dashboard, when i closed my back door on the left, the blinking went away, would anybody know if that is normal.
this key i know means something with the intellect key
i read the owners manual and it says nothing about this
 
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