Are the small compartments in cars safe to put spair keys in?

my car has these little square compartments on the front and back bumper and you have to use your finger nail to pop them out, i did that to mine and i put my spair key into it incase i lost my original and when i started driving then parked i checked to see if it was still there but i couldn't find it and the posibilitys are it could have fallen out OR slid further inside cus it actualy can so what do you think help me out!