It's cause that big magnet is pretty weak. You need one of these, just be mindful of any metal within 10 feet of ya.
https://www.ebay.com/itm/Industrial...674292?hash=item48dd411134:g:1TUAAOSwga9eIL0K
https://www.ebay.com/itm/Industrial...674292?hash=item48dd411134:g:1TUAAOSwga9eIL0K