Aftermarket car alarm installation

[NoisemakeR]

Hi, I was thinking of getting an aftermarket car alarm, something cheaper. But I wanted to ask, is it hard to install it by yourself? Of course with some basic electrical & mechanical skills. Also I've seen the keyless entry kits... are they hard to install? I've done some basic stuff like installing car deck, foglights, sub with an amp.
Any tips would be much appreciated.
later