Are there any safety issues with microwaves?
Battery contacts dirty.Grease and dust build up will cause the same problem.Best thing to do is replace it. EDIT Detectors wear out,especially old ones with dirt and grease build up coating contacts inside.Just replace it.
You only really need to use a torque wrench when getting the torque exactly right is crucial to the success of your procedure. One example is when you are replacing the head after a valve jobuneven torque pressure can cause the gasket to rupture or the head to crack or warp. If you don't have a good feel with a wrench, it can also be helpful in preventing over-tightening in less critical situations. I suspect that you won't need oneif you were working at the level where correct torque is critical, I think you'd know it.
not on the things you listed really . some jobs yes it is very important .
as stated by the previous answers only certain things need to be torqued. It is important to torque fasteners on anything that is safety related i.e. wheel lug nuts yes brake caliper bolts should be torqued. or anything that is to be sealed such as a valve cover gasket. the reason we torque fasteners is to make sue they they aren't over tightened beyond the fasteners limits or distort or crush the part being installed. An example of this would be if lug nuts are installed to tightly you can distort a brake rotor giving poor brake performance, damage the wheel or even stretch the stud causing it to fail when on the road.
