Please avoid paternalism when taking.
Air defence has different modes, how do you think is that Ukraine make ambushes to Russian planes with a Patriot of other means?
If the radars would be active the planes would see the anti aircraft system in its own radar.
The procedure is to use the radar in passive mode to avoid emitting signal and only activate it when you are going to shot, in order to direct the missile to the target.
This is the fire control you talk about.
When you know the target plane is close, and this is mainly visual, you activate radar and shot.
The ISR is mainly use to analysw the common routes of planes and place there the air defence for the trap
Please don’t get angry at others for pointing out your very obvious lack of knowledge and understanding of the subject at hand.
What you are describing is very entry-level understanding of anti-air vs SEAD/DEAD tactics based on fundamentally flawed assumptions and ideas.
Go to your closet airport and see at what distance you can positively identify commercial airliners on low level landing approaches and you will realise just how ridiculous your idea of relying on visual searching for modern air defence is. The opfor will need to be dropping iron bombs directly on your SAM site for visual searching to have any chance. Even cheap glider bombs would render your visual searching strategy irrelevant as good luck trying to spot even a bomber sized target 20km away at cruising altitude using your mk1 eyeball from the ground.
And unlike the Russians, the Chinese have been investing heavily in its support assets and toys. Any manned strike package going over Taiwan island itself will have dedicated Wild Weasel escorts.
That means even if my some minor miracle you did visually spot a strike package coming in, as soon as your radar lights up, it’s going to be the focus of multiple dedicated jammers with anti-radiation missiles incoming on your position very shortly afterwards.
That’s not to say it’s impossible to get a kill, just incredibly unlikely and expensive to do so. Since unlike the Russians, the Chinese will have true air dominance over Taiwan. Meaning any pot shots taken will attract massive and near immediate strike responses, so you are almost certainly going to loose the radar and launcher(s) that just engaged.
But the more likely scenario is that the PLA won’t even really heed to send in manned aircraft to over fly Taiwan island since they can easily strike at any point on the island from standoff ranges. Instead it’s massed drones that will be deployed to do the bulk of the search and strike missions, with manned aircraft acting as rapid response to deal with any unexpected events.
So in your example, the only things you can realistically spot would be drones, and if you light up to engage them, you can expect to be engaged yourself by manned and unmanned platforms long before you can pack up and scoot. If you don’t engage the enemy drones overhead, it’s very likely they will spot your hidden battery and shoot missiles at you anyways.
In a Taiwan scenario, the outcome will never be in doubt, the only question is how much it will cost the PLA.