Telephone
Used when the operator’s home is relatively far
from the greenhouse or so that a second or third
person can be called if the first does not respond.
This type of unit requires the use of an existing
or separate telephone line. A short time delay can
be installed in some units so that a short power
interruption is disregarded. Most units have a sensor
that activates the circuit, and a continuous tape with
several telephone numbers inscribed starts dialing.
If the first number is not answered after a short
time, the unit dials the second number, etc. When a
telephone is answered, a second tape is activated to
play a recorded message indicating an emergency.