It is impossible to online buy a cheap Non-contact Direct Current voltage tester pens.

In general, AC emits alternating magnetic fields which are easy to measure and radiate some distance. By contrast, DC emits a static magnetic field which is much more difficult to detect and measure as there are many competing sources of noise (e.g. Earth's magnetic field, remnant magnetism in cores/metals, etc). As a result, such a detection capability is not trivial - an AC tester could just use a regular coil of wire on a core like an inductor while a DC tester would need a very sensitive hall-effect sensor and a core that has little remnant magnetism to have any chance of working. Perhaps it would be hard to know the difference between a weak fixed magnet and a wire with DC flowing through. Worse still, this static field gets very small when the current flow is small - typical of low-voltage circuits.

For the same physically-related reason, DC clamp meters are more expensive than AC clamp meters because they are simply more difficult to realise and be accurate.

Sorry, but I don't think you will find cheap non-contact DC voltage detectors ... furthermore, such test devices are really only good for tracing things through walls as a rough indication and can't be relied on to make a good reading of voltage - for safety, you MUST measure the voltage by contact means and confirm.

- Gough

Very grateful for ur reply.

I researched that ac alternatives and the capacitance coupling allows the light n sound of ncvt testers while DC is constant current n can't.

Thanks very much 

DC voltage creates an electric field which is difficult to measure because any conductor can short out or modify the electric field. DC current creates a magnetic field which is also tough to measure accurately as Gough Lui  points out.

Electric field meters exist but as you mention, they don't tend to be cheap.

Here is an article on one way to measure electric fields...

https://www.eeeguide.com/dc-electric-field-strength-meter/#:~:text=The%20DC%20Electric%20Field%20Strength,currents%20sensed%20by%20the%20electrodes.

I was going to suggest you google "diy magnetometer probe" 

And this popped up 

I am skeptical... Must be a hall senor 

Thanks for posting, sorry I don't have an answer

scottiebabe  Okay.  I'll bite.  I ordered one from Amazon.  There is no Newark equivalent.  It should be here tomorrow.  3.7 stars with 25 ratings.  We'll see.

anniel747 It says it does it all.   We'll see what it does and doesn't respond to.  I suspect that one of the negative reviews on Amazon was because the reviewer didn't understand that you have to have current flow to create the magnetic field in electrical circuits.  Thanks for the reminder. 

I don't really understand the requirement. I can't see how for a "voltage tester" a potential difference would be detected with a pen (e.g. detecting an AA cell!).. presuming the request is to infer a DC flow of current, perhaps by the magnetic field?

I think a handheld pen method may need the user to frequently null it since if it moves, the weak magnetic field will change too, which doesn't help with a binary present/not present indication.

You could pack a circuit and little display in a pen. Below is a design that is reasonably accurate compared to commercial devices. However you'd need quite a high current  and be very close to the wire (or alternatively looped into an electromagnet) to get enough of an indication. Formula here: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magcur.html 

DC current sensors are low-cost (£10 ballpark) and are no-contact, but need the wire looped inside it. You could DIY that to not need the wire to be cut or disconnected, but it sounds like you want a ready-made solution. A ready-made DC current clamp with hinge is about £100, and can be connected to a cheap multimeter.

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What are you trying to measure? Yes, DC. But where, in what, and why?

Perhaps if there is slack the cable could be taped into an electromagnet of a few turns. A few mT could be created that way at reasonably low current (e.g. 1A) although I've never tried it!