10 Leds For Status

and i want them all to flash at the same time. thanks for the help

You can try like this to drive your extra strings of LEDs; depending on how much voltage each one of your extra LEDs need, you may need to break them up into more branches than the two shown here. If they need less than 2V per LED, then you can probably do 2 strings of up to 5. As long as they're in series, they should get the same current, up to the maximum number of LEDs per string. This is assuming your alarm output is normally putting out a positive voltage to turn on the LEDs rather than ground switching- if your current hookup has one end of the LED connected to a constant 12V, then you need to use a different setup. You can also try regular transistors; the main thing is to get them as matched as possible so that the current is mirrored in the strings of LEDs.

Just a note if someone uses this arrangement; if you use extra bright LEDs that run with higher voltages (Vf), then use a lower number of LEDs in each string, like 3 or 4 instead of 5. Otherwise, the battery voltage when the car is off might be below the level needed, and they won't light up to full brightness. Just break it up into additional strings by adding another transistor, and you can drive hundreds of LEDs at once if you really felt the need to create a spectacle. Saw a tractor trailor once that was lit up like Rockefeller Center at Christmas, all covered with LEDs. Not exactly sure what the idea was supposed to be, but it was gone before I could get a better look.