Chemical reactions can be detected by change in:
1. temperature color
2. overall mass of the products compared to the mass of the reactants
3. density of the products compared to the reactants

1. temperature color

3. density of the products compared to the reactants

Explanation:

In a chemical reaction, there is a rearregement in the atoms breaking and bonding different bonds producing a change in energy that means a change in temperature.

A chemical reaction can be detected by change in color in reactions as titrations, for example, where phenolphthalein is pink in basic pH and non-color in acid pH.

For the law of conservation of matter, overall mass of the products is the same to the mass of the reactants.

As in a chemical reaction you have a rearregement in the atoms, it is possible that this rearregement produce a better organization in the atoms increasing density or a poor organization decreasing density.

I hope it helps!

they it depends on if one believes about radioactivity, they make a geiger counter beep but maybe it was going to beep anyway electronics do wierd things all the time or it was programmed to beep near certain metals.