Voltage testers that are used for your home’s electrical wiring have lower requirements then those used to diagnose your cars charging system or other electronic devices.
For the most part electrical testers for 110 to 220 volt AC will test for the presence of current at a location. They are usually used to diagnose if there is a fault between the circuit breaker and the outlet or appliance, a mismatch in the wiring of a circuit and shorts.
There are times though when it is not possible to contact directly with the end of a wire to read if voltage is present but you still need to know if the wires are hot.
Non-contact electrical testers can test for the presence of a hot electrical circuit by touching the tester to or near a light, switch and some models that are integrated in stud finders will tell you if there is a hot wire inside a wall before you begin hammering or sawing to gain access.
Although they are not totally foolproof they will give you decent results and can be trusted for most work.
You should read the directions that come with your tester to better understand its limitations.
Noncontact voltage testers that can sense a hot circuit in a appliance or outlet are not suitable for testing the presence of live electrical wires in walls.
Units that can test for the presence of electricity in walls may be so sensitive that they give only general readings and may not allow you to track down a wire to a specific stud cavity.
You can expect to pay $15 to $80 or more for hand held units.