The COMPX Security Product DK4W Chicago Key Blank is a tamper-evident security product that is designed to protect your business' most important assets. The DK4W is a key blank that is printed with your business' unique security code and serial number. This key blank is designed to be used with the COMPX Security Product DK4W Chicago Key Reader. The DK4W is a tamper-evident security product that is designed to protect your business' most important assets. The DK4W is a key blank that is printed with your business' unique security code and serial number. This key blank is designed to be used with the COMPX Security Product DK4W Chicago Key Reader.