The COMPX Security Product DK4L Chicago Key Blank K-4-L is a tamper-evident security product that is designed to protect your business' most important assets. The DK4L is a key blank that is printed with your business' unique security code. The DK4L is a tamper-evident security product that is designed to protect your business' most important assets. The DK4L is a key blank that is printed with your business' unique security code. The DK4L is a tamper-evident security product that is designed to protect your business' most important assets. The DK4L is a key blank that is printed with your business' unique security code.