Enabling more complex alarm conditions, the EL042 EnviroMon PC data logging system from Pico Technology, is a system upgrade that automatically measure and records temperature, humidity and other parameters, and warns you when reading go out of range. The system is both flexible and economical: you can start off just recording a single temperature and expand it to monitor up to 40 sensors spread around a site. When the system detects an alarm condition, it can activate its built-in sounder, send a message by activating an external telephone dialer, or trigger up to three user-supplied alarm devices connected to its opto-isolated outputs. The unit has a rechargeable backup battery allowing it to maintain its alarm outputs for several hours in the event of a power failure. The unit enables a feature called a “deviation alarm”. You can now set up the system to monitor a number of channels as a group. The system can activate an alarm if any channel differs from the group average, or from any other channel in the group, or from the median of the group, by more than a specified amount. You can even define nested groups of sensors.