Advice needed for approach on RF car alarm remote

Hi,

I'm close to finishing the renovation of my classic car, but i'd like to protect it from theft with an alarm. Making an alarm with a shock sensor isn't that hard to pull off, but i want to be able to turn it off remotely. For this application, IR is not an option, Bluetooth is far too complicated and also not really an option, so i'm with RF. Because i don't have any experience with RF transcievers whatsoever, i'd like to ask some questions. I'm planning to make a simple RF communication between remote and alarm to arm, disarm, disable and enable(test) the alarm. Maybe i'll add a few other commands apart from the car alarm, but that's it. I think it's obvious, but data rates requirements are pretty much 0, and sending time per hour will also be pretty much 0. Interference is also not really a problem here i guess. A low power(off) consumption is preferred.

I have got a few questions:

  • Do you need an amateur radio license or whatsoever to even use and make this kind of stuff, or use certain bands? (more specifically to EU if possible, i live in the Netherlands) I don't have a clue about global rules regarding RF. I believe 100mW is maximum for 2.4Ghz but i'm not sure. The internet gives a shitload of info regarding RF but i can't find the info that matters to me.
  • What frequency should I use for this application? The range should be around 50m with obstructions. I believe commonly used(but maybe rather crowded) bands here are 27Mhz, 42Mhz, 433MHz, 2,4Ghz.
  • Does this RF n00b need to take any commonly made mistakes in mind?

Thanks for your time, Cheers!

You should probably just buy a remote controlled car alarm. You can get one for about $25 on eBay. It includes two remote controls.

If you really want to do it yourself I think in Europe you will use the 433 MHz ISM band. Many transmitters and receivers are available from eBay. Some transmitters are available in keyfob cases with several buttons.

I suggest you go look at the Moteino products, offered by LowPowerLabs online. They combine, effectively, an Arduino with a radio, 433 Mhz. and I think 915 MHz. also. The moderate powered ones are 20 mw. transmit, and they also sell some 100 mw. units, good for a half mile range. Te prices are very reasonable, they come with good library support. I'm using some right now in a home security system. They are compatible with both 3.3 v. and 5 v. circuitry (except for the radio part).

As for frequency, it is generally the case that lower fequencies give somewhat better range, so I'd go with 433 MHz. In the U.S. the Moteino products are legal without any license: I don't know about other countries.