Philips Sonicare DiamondClean Smart 9400 (HX9918/89) electric toothbrush with app and pressure sensor

The essentials

If you’re the type of person who wants your electric toothbrush to do more than just buzz a bit, the Philips Sonicare DiamondClean Smart 9400 is built around guidance. It pairs sonic brushing with real-time pressure feedback and a connection to the Philips Sonicare app for personalised coaching. On paper, that’s a strong combo if you’ve ever found you press too hard or you’re trying to improve your brushing routine rather than just replace a manual brush.

Key features that matter in daily brushing

The DiamondClean Smart 9400 offers 4 brushing modes and 3 intensity levels, so you can adjust the feel without changing the whole setup. The headline “smart” bits are twofold:

• Pressure sensor with light ring feedback: the light ring flashes if you use too much pressure. That’s useful because even a good brushing technique can get undermined by over-brushing.
• Brush head detection: the handle can recognise the brush head, which helps keep the experience consistent (though, like most systems, it still relies on using the right heads).

Then there’s the app connection. When you link it to the Philips Sonicare app, you get personalised guidance designed to help you maintain and improve your habits. Whether you’ll find the app genuinely motivating will depend on how much you like feedback from your phone while you brush—but for many people, that “nudge” is exactly what turns an electric toothbrush into a routine.

What stands out (and what you might need to be realistic about)

Philips positions this model as an advanced sonic toothbrush, with claims around plaque removal and gum health, plus stain removal compared with a manual brush. Those are impressive figures on the listing, but it’s fair to say results vary quite a lot depending on technique, how regularly you brush, and whether you actually adjust to the pressure feedback.

A more practical limitation to keep in mind: if you prefer a very simple toothbrush and don’t want to involve an app, you may not get full value from the Smart part. Also, electric toothbrush systems usually live and die by brush head compatibility and replacements, so it’s worth thinking about ongoing parts before you commit.

Who it suits best

This toothbrush makes sense if you’re:

• trying to improve your brushing technique (especially pressure control)
• someone who likes structured options, like switching modes and intensity levels
• happy to use an app for guidance rather than treating brushing as a purely offline task

It’s also a good match for adults who want a more “coached” experience—more than what many basic sonic brushes provide.

Where it shines in real life (a quick example)

Imagine it’s morning, you’re half-awake, and you tend to press a bit to “get it done”. With this model, if you push too hard, the light ring flashes. You automatically ease off, which can make the brushing feel more comfortable while still covering your teeth. After a few sessions, the app guidance can help you notice patterns—like brushing for too short a time or not covering certain areas as consistently.

That little feedback loop is often what people end up valuing most: not just cleaning, but sticking to the habit.

Things to check before you buy

Before purchasing the Philips Sonicare DiamondClean Smart 9400, check the basics that affect day-to-day ownership:

• Power plug: the listing notes it includes a UK 2-pin bathroom plug for bathroom use. That’s helpful for UK shoppers.
• App experience: make sure you’re comfortable with the idea of personalised guidance via the app.
• Replacement heads: since this is a system with brush head detection, you’ll want to be confident you can source the compatible heads when needed.

Final verdict

Final verdict

It’s a sensible buy if you want an advanced sonic toothbrush experience with pressure feedback and app-based guidance, and you’re willing to use those features rather than ignoring them. If you love the idea of tuning modes/intensity and getting coaching on your routine, the DiamondClean Smart 9400 is likely to feel like more than a simple upgrade.

It may not be the best fit if you prefer a no-phone, no-frills toothbrush, or if you’re looking for something purely straightforward and low-maintenance in terms of system components. In that case, you might feel the “Smart” features are more complexity than you need.

FAQ

FAQ

Is the pressure sensor meant to stop over-brushing? It’s designed to give real-time feedback: the light ring flashes when you use too much pressure, so you can ease off.

How many modes and intensity levels does it have? It offers 4 brushing modes and 3 intensity levels.

Does it need the app to work? The listing emphasises app connection for personalised guidance, so the Smart guidance experience depends on using the app—though the product is still an electric toothbrush regardless.

Does it work with brush head detection? Yes, the listing states it has brush head detection, which helps keep the experience aligned with the correct heads.

What plug does it include for UK bathrooms? The listing says it contains a UK 2-pin bathroom plug. Packaging may vary.