alarm/remote start repetitive topics

Some topics come up with boring repetition so I'm  trying to get the record straight.

Remote start on vehicles with MAGIC (laser) KEYS e.g. current Mercedes:- FORGET IT!

Door contacts that trigger the alarm:- If your alarm is giving out spurious triggers at certain time intervals or telling you a door is open when it isn't you probably have a late model vehicle with a body control unit aka BCI (Honda), BCU on some American cars, GEM on Fords,  BSI on Peugot/Citroen.

This unit goes to sleep (ie internal circuits are "shut down" to conserve battery power, quick check leave door open with domelight on, if it shuts down after about 10mins you have one). These units self check on waking up, e.g. is a door open ? This surges a spike through the system triggering the door/trunk contacts etc. The ONLY correct answer is to diode block between each door contact and the CPU thus preventing the "self checking spike" (I'm sure there is a better technical expression for this but I don't know it) reaching the alarm. Yes I know there are exceptions, Golf/Jetta IV, Fiat Punto where the trunk light not the domelight will cause grief but that knowledge comes with experience.  A link to THAT DIAGRAMME was given by flobee4 on Aug. 13th (Thanks).

Out of interest biggest culprits are Ford, VW and some Renaults. BMW, Mercedes and most Japanese don't seem to suffer.

Tach sense:-  The usual methods are:- coil, back of rev counter/tach injector port, engine management CPU, OBD II socket (some Toyotas, all current BMW, diagnostic (engine bay) socket some Mercedes.

The first two are out on most late models (no coil and inst. panel data linked e.g. Ford Focus).

If you have any doubts about this use an inductive or can sensor from Directed, Fortin, etc. They work well and they cannot damage the vehicle.

Great topic, here's my $0.02:

Ideal locations for antenna:  Usually top center of the windshield BELOW the tint line; No, you usually cannot "double" the length of the manufacturer's antenna to "double" reception; and no, you cannot add a second antenna to place in the rear of the car if the brain will only acknowledge/interface with ONE antenna.

Exceptions: certain manufacturers (Compustar) request antenna to be placed in top left corner of windshield -- it's highly recommended you follow these instructions to optimize reception;

Nissan/Infinit Smartkeys:

This has been discussed indepth, many times, a search will reveal all the details, but the gestalt is that you can wire the vehicle up to remote start, however when you enter the car, you'll have to shut it down, and then manually restart with the push button/steering column lever.  Slightly inconvenient, yes?  Could you have opted to not purchase a vehicle with Intellikey/Smartkey in order to have more convenient remote starting capability -- absolutely.

And finally, if you don't know what any of the following things are, DO NOT install your remote starter by yourself, have a pro do it:

a) VMM

b) DMM

c) voltmeter/voltage multimeter

d) digital multimeter

e) multimeter