Selecting and environmental alarm

If an equipment malfunction or power outage occurs in an agricultural facility when nobody is there to notice, the environment can quickly become deadly to animals or plants. For example, failure of a greenhouse heater on a cold winter night could freeze plants. Ventilation failure on a hot summer day can kill animals. To help prevent such losses, a monitoring system can be installed and programmed to send an alert if critical environmental parameters reach dangerous levels. With the right sensors, alerts can also be sent out in the event of ruptured water lines, power outages, and/or other equipment failures. A monitoring system will hopefully never be used, but if it is, could easily pay for itself the first use. Functionality, reliability, safety, false alarms, and costs should be considered in selecting an alarm.


Alarm functionality

An alarm can be a stand-alone device or an integrated part of a plant or animal facility’s environmental controller. A stand-alone alarm will have its own sensors and base unit to send alert signals. These are commercially available from La Crosse Technology, Sensaphone, Monnit, and others. Manufactures of computerized control systems offering integrated alarms include Wadsworth, Argus, Link4, Micro Grow, Priva, and others. If you already have a computerized control system and are thinking about an alarm, it is worthwhile to investigate if there is an alarm feature that can be activated.

The number of parameters to be monitored is an important consideration when choosing an alarm system. Each parameter monitored; temperature, humidity, CO2, etc. requires its own sensor and input. Basic alarm systems are limited to sending out alerts. More advanced features include data logging and real-time monitoring of current environmental conditions. Alarm systems with the most functionality offer remote monitoring and control of environmental set-points. Alarm systems send alerts by phone call, text message, and/or email. Find out from employees who will receive potential alerts which method of communication will be most effective.



Alarm systems consist of sensors and a base unit that communicates with the outside world. In some alarm systems the sensors and base unit are wireless while others are hard-wired. Without question, a wired system will be more reliable because there will be no connectivity issues. The advantage of wireless systems is there is no need to hide and secure wires. To install a hard-wired system it may be necessary to dig trenches to bury the wires.

The base unit can communicate through a phone landline, cellular communications, or Internet connection. A landline is the most reliable connection as it will continue to function even when the power goes out. Unfortunately, many agricultural facilities do not have a landline. The next best thing is sending messages through cellular communications assuming a strong signal. In the event of a power outage, a cellular system will require a battery backup. An alarm communicating with the Internet will be the most vulnerable to power outages. An additional battery backup is required for the modem.



Any pathway for communication with the outside world opens up an entry point for cyber-attacks. Basic alarm systems limited to sending information carry the lowest risk. When two-way communication takes place, for example to control environmental conditions remotely, the risk of attack increases. Phone lines and cellular connections are less likely to be attacked than an Internet connection, but there is no completely safe connection. Hard-wired alarm systems are safer form a security standpoint because anybody with the right equipment can pick up a wireless signal. Use multiple layers of security such as long passwords, firewalls, and an independent network for the alarm through dual network interface cards in the computer. Hackers target vulnerable systems, not necessarily large operations. A devious individual may hack a system and simply adjust the temperature set point from 65 degrees to 120 degrees.


False alarms

Limit false or delayed alarm messages by ensuring reliable sensor readings. Multiple false alarms will cause individuals to begin ignoring alarm messages. For example, direct sunlight on a temperature sensor may generate a false alarm for high temperature. Do not allow direct sunlight, heating vents, or cooling pads to interfere with temperature reading. Place the sensor in an aspirated radiation shield to ensure a representative measurement. The base unit and any other electronics should be protected from the elements as well. Be careful not to use the battery backup in such a way that it fools the system into thinking the power is on during an outage.



Wired base units cost more than wireless, but they usually have more functionality, such as built in data logging. Systems that log data usually require a computer, adding to the cost. Most companies offer free software but some do not.

Operational costs include electricity, telecommunications service, and annual fees if you are data logging in the cloud. To properly maintain an alarm system it is most important to replace the batteries (average every two years) in the sensors. Batteries that are not replaced in the recommended time frame can leak and damage the sensor.

Infrastructure costs, such as the purchase and installation of cables, exist for hard-wired systems. In some cases, especially where structures are already constructed, it can be less expensive to purchase a complete wireless system than paying to bury wires.


Dr. Peter Ling is an Associate Professor and Extension Specialist in the area of controlled environment plant production. He can be reached at 330-263-3857 or This column is provided by the OSU Department of Food, Agricultural and Biological Engineering, OSU Extension, Ohio Agricultural Research and development Center, and the College of Food, Agricultural, and Environmental Sciences.

Luke Power is a Research Associate in the OSU Department of Food, Agricultural and Biological Engineering.


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