Reed contact resistance (CR) is the DC resistance caused by the resistance of the gap between the dry reed itself (body resistance) and the switch terminals. Most of the contact resistance is found on nickel/iron dry reeds. Their electrical resistivities are 7.8x10-8Ω-m and 10.0x0-8Ω-m, respectively, compared to copper's resistivity (Cu's resistivity is 1.7. x10-8_Ω-m) This is quite high.
In general, the contact resistance of the entire reed switch is approximately 70 mΩ, and the resistance of the gap between the switch terminals is actually about 10 to 25 mΩ. On reed relays, the relay pins are usually made of nickel/iron to improve the overall magnetic performance, but this also increases the resistance of the reeds. The added resistance is about 25 to 50 mΩ.
A reed switch as shown in the figure above is an example of the contact resistance formed by the resistance of the body of the reed body and the resistance of the gap between the switch terminals, and the value of the resistance value in ohms.