Memory tells me that they are "code" operated on HAL -- as in, you enter a series of numbers on a keypad to access the safe. I consider those to be much safer than the "credit card" ones.
Just make sure that the code you come up with is easy to remember for you and your companion(s).
On a recent cruise with my sister-out-law we went through this elaborate process of establishing a code that we could both remember. We decided on the last digit of the years of birth of our kids. As in 5,7,9,1 ... then she couldn't remember when MY kids were born and I couldn't remember when HERS were.
Never mind that we are Godmothers to each others' kids.
pamda -- CruiseMates Utility Infielder
p.s. When my husband and I travel together, it's easy. We just use the PIN for our MAC card, followed by 00's if the safe wants more than four numbers.