The Columbus Instruments Opto M4 is our latest implementation of our popular multi-channel activity monitor that supports a variety of sensor lengths and configurations (successor to the previous generation's Opto M3). Up to 32 channels are supported providing both ambulatory and total counts for each channel. Communication is via serial RS-422 using the CI Bus protocol (MDI Software). Cabling is simplified by the use of 8 channel hubs that connect to the Opto M4 with 25 pin shielded cables. Sensor cabling uses convenient RJ-45 connectors and sensor power is supplied from the Opto M4 controller over the signal cables so no external power supplies are required. Unique to this system is the ability to re-arrange sensors to change the coverage of each cage. For example, a 20 cage X axis only system can be reconfigured to measure X and Z axes in 10 cages. Additional sensors and brackets can be purchased to expand the number of cages or coverage per cage. The Opto M4 can also be integrated with other CI Bus compatible instruments to incorporates multiple measurement parameters such as feeding mass/bouts, drinking volume, VO2 and VCO2, etc.