By "dangerous" I assume you are talking about if you lose the card or it is stolen. If you lose an ATM card a person can only get to your money if they know or figure out your PIN. If you lose your debit card they could use the card for purchases just about anywhere. BUT there are limits to how much you can use your debit card in one day. Basically, you need to weigh your needs and see which card fits you best. I could't survive without my debit card. I use it for everything from vacations to weekly supermarket trips. I would rather carry my debit card than cash with me. I tend to lose cash, but I always know where my debit card is. I can't recall offhand what the max. limit per day is $500 or $1000 unless you call the bank and ask them to change it. This would prevent anyone who found your debit card from spending thousands of your dollars. On the other hand ATM cards are quick and easy to get cash and if you lose it chances are no one will take your money. There is, of course, the issue of people stealing PIN numbers and then taking your money. It is your choice about which is more "dangerous".
