You can keep fire doors Open and still comply with fire codes with these simple magnets

At left is a Fire Door by code it must be closed at all times but as you can clearly see some one set a brick in front of it to hold it open . A clear and major fire code violation which can get you written up by code enforcement when they inspect your property. But there is an excellent device on the market to prevent this known as a magnetic door holder .
  The unit which  a sample of which can be seen in the bottom left picture shows one style of unit which is mounted on the floor behind the door which holds the door in place using an simple 12 -24 volt DC  or 24-120 Volt AC electromagnet  which a relay in the fire panel releases when the fire alarm activates allowing the door to drop closed. The units draw very little power and can be powered in some cases off of a plug in transformer. The magnet attaches to floor or wall behind door then the  round armature piece attaches to the door.
The units are inexpensive around $150.00  or less plus installation and are easy to wire in and require no maintenance. I have installed hundreds of these units on customers property's to help prevent problems with doors getting propped open especially in apartment buildings. There are also high end units  available where the closer  can be holder and closer in same unit but I tend to avoid them as they are maintenance intensive especially in buildings where people hang on them and force them closed.
Electromagnetic   door holders have been around for many decades now and you may have experienced them if you where ever in a building when fire alarm activated like a hospital and all the doors started closing on there own.
 One word of caution these units must be wired to an independent power supply not the fire panels  power supply to prevent problems of the fire alarm failing to operate during a power failure.