There are many varieties of train detection and signal control systems commercially available for the railway builder. The range is tremendous, from relatively cheap signals that change state when a magnet fitted to the train passes a reed switch under the track, to advanced radio transponder systems with vehicle recognition which `reads' each item of stock as it passes over (or under if fitted under a bridge or tunnel) a small sensor in the track, such units can control signals interlocked with points and can be made to stop a train prototypically, slowing and stopping for a defined time at a station or signal, before proceeding to on its allocated path but only if the path ahead is clear, the points are correctly set and the signals are in the trains favour. Interlocking signal control with points can be easily achieved with an electric signalling system but can become quite complex when interlocking with mechanical control systems (Mechanical point rodding and/or signalling equipment) some of the available units are supplied with instructions/diagrams for interlocking points with signals and signals with each other, EG: Home and related Distant signals change state dependant on the position of the points controlled by the operator, other signals will not be able to change state if they would conflict with the points and signals currently set. There are control units suitable for almost any eventuality, especially when using several different units to suit the particular layout and operational characteristics required.

There are a vast number of colour light signals available in all popular modelling scales which can be easily used with the majority of bought signal controllers, most controllers operate at either 12v DC or 16-18v AC, some colour light signals will require the addition of a resistor to limit the current to the signal. Most signals have one 0v (Ground) wire and one wire for each signal lamp, these types are easily controlled and can be manually switched easily, There are some signals that are operated by reversing the polarity across two wires to change the signal aspect, this type can be awkward to setup on some control units so it is worth checking that the controller you are going to buy is suitable for the type of signals you are using.

There is also a reasonable range of semaphore signals available from 2mm scale upwards both as kits or ready built, that can be operated with solenoids or point motors, Some control units will be better suited to such work than others, and everyone makes them differently so if you are unsure check with the manufacturer. There are even some manufacturers out there that have been known to modify units to suit a particular purpose. (EG: providing a board with heavy duty output transistors fitted to enable it to hold several signals `off' (solenoids required higher current)