Review: SonarPen: Battery-less Smart Stylus for iPad (Kickstarter)

I get many requests to review styluses and I would usually reject the offers because most styluses look and work quite similarly. This time I made an exception for the SonarPen because it looks quite intriguing.

This stylus is designed for the iPad and connects to the iPad via the 3.5mm audio jack. It's supposed to support palm rejection and pressure sensitivity. SonarPen utilizes the iPad's high-res analog-digital-convertor in the audio jack for the pressure detection. The pressure data is supposed to be sent back to the tablet via the audio jack. That's something new to me.

This is the prototype stylus that I received. The inventor Elton Leung spent 3 years on it and has finally released it on Kickstarter to raise funding to manufacture the styluses. At the time of this review, the campaign has already received 651 backers.

The stylus is attached to a 50cm cable that you can wind up and keep together with the body. Different colours options are available for the cable.

There's a plastic disc tip at the front, and one shortcut button on the side. Depending on the app you use, you may be able to assign certain functions to the shortcut button.

The disc is connected to the tip by black conductive silicone. Inside that silicone is probably something stronger because I could feel something there.

When drawing and writing with the stylus, the disc will be flat against the screen and when lifted goes back to its original position. The prototype that I had had some filings at the edge of the disc that were not filed off. So it looks a bit rough. Anyway, this is a prototype. Hopefully the actually products will look more polished.

Here's the size and length comparison between SonarPen to the Apple Pencil and Adonit Pixel Pro. SonarPen is a bit thicker.

The build quality feels quite solid enough. Surface is matte and nice to hold. The cable is long enough to prevent any entanglement. Weight is good, a bit on the heavier side but not too heavy that prevents drawing for long period of time.

Drawing performance

Since the SonarPen is really a capacitive stylus, it works on all tablets: Android, iPads and Windows (not really on touchscreen laptops and 2-in-1s though). The features that it advertises, pressure sensitivity and palm rejection, only works on the iPad.

Pressure sensitivity support depends on the app that you use and right now, the only two apps that are supported are Zen Brush 2 and ZoomNotes. The stylus has to be paired with the app for it to be recognised.

Here's a quick sketch I drew with Zen Brush 2. Pressure sensitivity works well enough. With Zen Brush 2, you also have the option to choose different levels of pressure sensitivity. At the Medium setting, I was able to create a thin line with a touch touch.

Palm rejection is not flawless though, I did get some stray marks when resting my palm on the screen while drawing. But it's not as bad compared to other drawing apps I've used.

The plastic disc moving on the surface has some friction so it's not too slippery and offers good control.

ZoomNotes offers pressure sensitivity support also but the line variation isn't as obvious compared to Zen Brush 2. The strokes aren't as smooth either, and that's mostly because of the app not the stylus.

With other apps, SonarPen just works as a "dumb" stylus, pretty much like your finger. The good thing here is the disc tip is extremely accurate. There's no parallax, no offset. The line always appear directly beneath the tip. The performance is essentially no different from those disc-tip styluses from Adonit.

With other apps, palm rejection does not work as well compared to Zen Brush 2 and ZoomNotes. I had quite a few stray strokes (bottom right) with Wacom Bamboo Paper.

In terms of responsiveness, it's as responsive as if you were to use your finger.


The overall drawing experience is quite nice when used with Zen Brush 2. I was able to create the lines the way I want them to be. The main advantage is there is no parallax and offset like those 1.9mm tip battery-powered styluses but the "downside" is there's a disc tip in front. The disc tip is replaceable though, and a few replacement tips will be included in the box.

I was told that there will be a magnetic pen holder included that you can attach to the iPad. But if you're using an iPad case, I not sure how you can still attach that holder to the side. Another concern that I have is what will happen to the disc if it gets knocked around because it's so exposed. This stylus has no cap.

I thought the cable would be a hassle, but it's really not an issue. It would be great if there's no cable but if it can provide pressure sensitivity support that works well, I'm fine with it. And that brings me to the next point. It would be great if there are more apps that support this stylus. Right now, only Zen Brush 2 and ZoomNotes support the stylus. The more popular drawing apps like Procreate and Medibang Paint Pro for example do not support it, yet.

As for the palm rejection implementation, I can't say that I'm too surprised that it's not perfect. I haven't seen any perfect implementation of palm rejection other than on the Apple Pencil. That's basically the downside of capacitive styluses. I'm quite used to lifting my palm to draw with these styluses so it's not too big of an issue to me. But I know there are people who find the lack of palm rejection to be a deal breaker. Palm rejection works slightly better with supported apps.

Update: Elton Leung told me that Zen Brush 2 developers will be building better palm rejection into future versions of their app.

You can certainly use this stylus to take notes. I prefer to use Wacom Bamboo Paper to take notes because it's able to capture my handwriting accurately. There's no lag when it comes to taking notes.

Oh, another downside is, you obviously can't use your 3.5mm earphones while you're using this stylus. And if Apple removes the 3.5mm audio jack in the future... Let's just hope they don't do something that silly.

To check out more details or get a SonarPen for yourself, visit the Kickstarter page at

Campaign ends 24 March 2018, Saturday.


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