Tell us about yourself!
cheap ones and those installed on a dirty surface or a place that's not flat may fall off. The one I mentioned by Masterlock has a very strong magnet. I've been using these for years with great success.
No one will see me install it. I work in my garage.
I put a spare key in my holder. You're right, wouldn't be to safe to step out your car and place it on the car in full view of everyone.
A lot of time and trouble when you can buy a Master Lock magnetic key holder for $3.52 from Amazon. https://www.amazon.com/Master-Lock-207D-Magnetic-Keycase/dp/B003WXGLS2/ref=pd_lpo_vtph_229_bs_lp_tr_img_2?_encoding=UTF8&psc=1&refRID=8B2P3PCC8EGXJKJN8FQ7
Tools + Supplies
You shouldn't use a yellow wire nut for 5 #18 conductors. You can use two yellow with a jumper wire between the two. To be technical, you don't twist wire together for a wire nut. Hold the wires, insert into nut and twist the nut. Then wrap black electrical tape around the nut and wire to secure it.