Conventional panels have been around ever since electronics became small enough to make them viable. They are no longer used frequently in large buildings, but are still used on smaller sites such as small schools, stores, restaurants, and apartments
A conventional system employs one or more initiating circuits, connected to sensors (initiating devices) wired in parallel. These sensors are devised to decrease the circuits resistance when the environmental influence on any sensor exceeds a predetermined threshold. In a conventional system the information density is limited to the number of such circuits used. At times, a floor plan of the building is often placed near the main entrance with the defined zones drawn up, and LEDs indicating whether a particular circuit/zone has been activated. Another common method is to have the different zones listed in a column, with an LED to the left of each zone name.
The main drawback with conventional panels is that one cannot tell which device has been activated within a circuit. The fire may be in one small room, but as far as emergency responders can tell, a fire could exist anywhere within a zone. The same applies to coded panels, which nowadays are no longer made, but can be found in old systems. These, if the decision is made to keep them, are "grandfathered" in under NFPA regulations.
(Note: The larger the system the less competitive the price mainly due to higher installation costs.)