Phone HUD vs OBD HUD: Which Head-Up Display Should You Buy?

Short answer: if you want turn-by-turn navigation at eye level, a phone-reflection HUD does that for little money, as long as you use a navigation app with a HUD or mirror mode. If you want your speed and engine data on the windscreen with no phone involved, you want an OBD HUD, and your car needs an OBD-II port.

The two kinds of car HUD

Phone-reflection HUD

A cradle with an angled, see-through panel on top. Your phone lies face-up in the cradle and its screen reflects off the panel into your line of sight. Nothing plugs into the car. It shows whatever the phone shows, which in practice means navigation.

OBD HUD

A small display unit that plugs into the car's OBD-II diagnostic port, usually under the dashboard by your knees. It reads data straight from the car (speed, RPM, sometimes coolant temperature or fuel use) and projects it onto the windscreen or a film you stick to it. No phone needed, but no maps either.

The catch with phone HUDs: the mirror image

This is the part most listings leave out. Because you are looking at a reflection of your phone, the image reads back-to-front. A normal map app, including standard Google Maps and Apple Maps, looks reversed on the panel.

The fix is simple: use a navigation app with a HUD or mirror mode, which flips the display so the reflection reads the right way round. Search "HUD" in the App Store or Google Play and you will find several, free and paid. Check the app works in your country before you rely on it.

The catch with OBD HUDs: compatibility

• Your car needs an OBD-II port. Petrol cars sold in the US from 1996, and in the EU from 2001 (diesels from 2004), have one.
• Some cars, particularly hybrids and EVs, do not report every value over OBD, so a unit may show speed but not RPM or fuel data.
• The cable runs from under the dashboard up to the display, so it is a small install job rather than drop-in.

Daylight: both struggle

Every reflective HUD, phone or OBD, is at its best at dusk and after dark. In direct midday sun the image washes out. Turning your phone to full brightness helps a phone HUD; OBD units have their own brightness sensor but are still weaker in bright sun than at night.

Side by side

Which one should you buy?

• You want navigation at eye level and you are happy to install a HUD-mode app: phone-reflection HUD.
• You want a speedo on the windscreen and never want to touch your phone in the car: OBD HUD, after checking your car has the port.
• You mostly drive in bright daylight: be realistic about either. A good phone mount at eye level may serve you better.

What we sell

We sell one of these: the Car Phone HUD Display, a phone-reflection HUD. It does not plug into the car and needs a navigation app with a HUD or mirror mode. We do not sell an OBD HUD. If that is what you need, buy it from a shop that lists OBD compatibility for your model.

Want navigation at eye level without a HUD at all? A dash phone mount puts the screen high enough to glance at, with no mirror-mode app needed.