Most hotels today use credit card-like keys to electronically open hotel room doors. They are safe and easy to use. Unfortunately, Onity Security a company that provides such keys for more than two hundred hotel chains around the world including Hyatt Hotels has a security flaw that has recently been exploited by hackers who take a cheap electronic device and attach it to the DC port found at the bottom of the outside part of the locking mechanism that will automatically open the door to the hotel. This device uses the same technology that permits the hotel management to open the lock with a master key. Already there have been a number of hotel burglaries particularly in the Houston area that appear to have used this device.
If you are travelling you should ask the front desk clerk if the hotel uses Onity Security locks and if they have fixed the vulnerability of those locks. You should also make sure that you do not store expensive items in your hotel room and use the hotel safe for storage of important items such as jewelry and cash.