The green light flashing all the time could just mean that the unit has gone off before; please press the test button to reset the unit. I hope this helps.

A smoke alarm should be placed near the bedrooms and then at least one or more on every level of the home to ensure that you are alerted to a fire as soon as possible. If someone sleeps with the bedroom door closed, than an alarm should be placed in the bedroom as well. The range is 100 feet or more depending on the number of walls and floors the signal must go through. Remember to set the dipswitch on each alarm to the same code before installing the batteries in the units. Then push the test button of the first wireless alarm and it will sync the remaining wireless alarms if all the codes are the same. If all of your wireless alarms do not sound, then check to ensure that the codes are set properly. Here is the link to the manual for the wireless alarm model 900-0201
http://www.kiddecanada.com/utcfs/ws-463/Assets/900-0201%20Manual%20English.pdf