CF card unit is just like the regular compact flash card When the CF card transmitter goes over the preset range, the master unit will emit a warning tone immediately Acts as a burglar alarm and a reminder Can be put inside CF card slot without other's awareness Offers safety, security, and peace of mind Automatic battery saver function Auto power on and auto sleep functions Adjustable range setting from 0.5 to 6 meters An active wireless alarm Patented in the USA, Taiwan, Japan, mainland China, and more Size: Pen type master unit: 4.9 x 1.1 x 0.7 inches Sub unit: just like the real CF card (1.68 x 1.49 x 0.14 inches) Weight: about 55g Power: Master unit: 1.5V DC (AAA/UM-4 battery x 1) Sub unit: CR2025 lithium battery