Is the caster of Zone of Truth aware of the save result?

If I cast this spell, will I be able to tell whether the target saved or not?

The spell level and therefore the DC will be too low so my intention it to use it for negotiations where the target and myself both decide to fail it to make the negotiations more reliable.

In case I can’t be aware of the result (which makes the spell completely useless since everyone can save it), is there some other spell that can be used to reliably prevent lies?