in the drawings the numeral 1 designates a panel housing in which the respective units 2 , 2 are mounted . each unit consists of a transparent plate 3 opposite the outer face of which is mounted a bank of light sockets , in which the lights 5 , 5 are mounted . these lights are preferably in increments of four , so that the possibility of all of these lights being burned out at the same time is quite remote , and consequently the plate 3 will be illuminated when the alarm is activated . a spring loaded shaft 16 extends from the panel plate 3 to the switch 8 , which is a solenoid operated switch actuated by the coil 14 when sensor 12 is activated , and which is normally in open position and movable to open position , once it has been closed , only by deactivation of the solenoid , manually , by operation of a remote switch 4 . adjacent the switch 8 are the diodes 6 , 6 which give directional control to the circuit passing therethrough to the alarm means 7 and sensor 12 . the units 2 , 2 are removably mounted in the panel board 1 and normally the plates 3 are flush with the surface of the panel board 1 , with indentations at the openings in the panel board to receive the units , which provide means for a finger grip on the sides of the units for easy removal . the switch 8 is manually opened , and the sensor 12 , of any desired character , is located remotely from the panel 1 , such on a water jacket of a stationary engine ( not shown ) and is designed to be activated at a predetermined condition , as by overheating of the water in the water jacket , and to transmit a signal to the solenoid 14 , activating the solenoid which will close the switch 4 and illuminate the lights 5 , 5 , and activate the audio alarm 7 . the attendant on duty at the location of the panel board 1 may then silence the alarm by pressing on the plate 2 , which will open the switch 8 , breaking the circuit to the alarm 7 . the lights 5 , 5 however , remain on , through the lines 11 , 9 , so that the attendant knows the cause of the alarm has not been corrected . when the attendant goes to the area of the sensor 12 , and corrects the condition causing the alarm , such as supplying water to the cooling jacket , the switch 4 , located in the area of the sensor 12 , may be manually opened , to turn off the lights , indicating a correction of the trouble . by returning to the panel board and depressing the plate 2 of the pertinent unit , the switch 8 is again closed and the alarm reset . the circuit through each unit 2 is through line 17 , to lines 9 , 13 . the switch 8 is closed by manually depressing the panel 2 , moving the shaft 16 against the pressure of the spring 18 , and against the switch 8 , closing the circuit to the sensor 12 through lines 13 and alarm 7 in line 13 . the diodes 6 , 6 maintain the circuit in clockwise direction only . the switch 4 , located remotely from the panel 1 , is open until the sensor 12 activates the solenoid 14 , closing the switch 4 and illuminating the lights 5 , 5 , the circuit being through lines 17 , 9 , 11 and 13 . when the sensor activates the solenoid , both the alarm and the lights will be activated . depressing the panel plate 3 opens the switch 8 , breaking the circuit through the sensor and alarm , but the circuit through lines 17 , 9 , 11 , 13 continues , leaving the lights 5 illuminated . when the attendant finds and corrects the fault , the switch 4 is manually opened , turning off the lights , and upon return to the panel board , the plate 3 is again depressed closing the switch 8 , and resetting the alarm system . as many units may be installed in the panel board 1 as desired , each having the dual circuits above described , all parts , other than the sensor and the remote switch , being located in the unit mounted in the panel board . where trouble is experienced in the individual unit , it may be quickly and easily replaced , indentations 19 in the unit housing opening providing space for a finger grip on the unit to withdraw same from the panel board . terminal connections as 20 are mounted on the rear of the housing 1 to receive the wires from a source of power and leading to the remote sensor 12 , alarm 7 and switch 4 . a testing set 15 , having all the elements of the unit above described , may be mounted in the panel board 1 , and a switch 16 , simulating a remote switch , provided in the panel board 1 , so that the circuits may be tested at the panel board .