You would need a 1200 (AKA 1K2) Ohm resistor for this.
You have 10 mA, 13 volts and 1.4 volts as a reference.
13 volts minus 1.4 volts == 11.6 volts to drop.
U=I*R; R=U/I; 11.6 / 0.01 == 1160, makes a standerd value of 1200 Ohm.
10 mA is not a lot, is there a need to use those optocouplers ?
You could connect directly to your Arduino.
Or use some transistors to boost the signal from your alarm system.