There is a high chance that Jagex watches people who alch there.
Maybe alching at duel arena hospital would be less suspisious and there is no randoms either
It won't let you alch in the fight caves. Your best bet is to go to a pc world and dd on people in the bank. You'll be on the bottom of the pile probably (certainly if you change your IP the 4th section is higher i.e. xxx.xxx.xxx.200+) so nobody will notice you and you wont get reported. I think that if you get a 6 hour logout Jagex will look at what you were doing on your account since you last logged, so run a batch file that shuts down your computer after about 5-5.5 hours or so.
I personally suggest that you use murgee random mouse clicker. It offers random delay times, random pixel offsets, etc. Then just pick a location with no randoms, such as pest control bank or games room and you should be fine.
Pest controls bank is the only bank location that has no random events. What i'd do is set up two bots, that take breaks when the other starts, one alching and the other training a stat done at a bank, for instance fletching. Less chance of a ban.
If you're going to be at your computer while alching, whether or not there are randoms does not matter. Just have an open window in the corner of your screen. Or shit, don't bot if you don't know how to do it right.
Ive botted alot at the PC bank just go to a world with over 300-400 people and sit on top of someone and alch away, don't even need to talk in there most people are silent anyway getting on with things.