Giving an Old Phone a Second Life: How an Unused Android Device Can Serve as an Advanced Wireless Car Display

Facing a failing or malfunctioning head unit in a vehicle can quickly turn a daily commute into an exercise in frustration. For many drivers, the ideal solution involves securing a dedicated screen for turn-by-turn navigation and music playback without the hassle of unpocketing and plugging in a primary smartphone every time the ignition turns over. Recognizing this common automotive pain point, tech journalist Anurag Singh found a clever and cost-effective workaround using an older, second-hand device: a Samsung Galaxy S21 FE.

Rather than paying hundreds of dollars for a brand-new aftermarket stereo system or professional dashboard repairs, Singh repurposed the aging smartphone to act as an external display. Because the device is a few generations old, second-hand models can be acquired for a fraction of their original retail price. While it may no longer be anyone’s daily driver, its high-resolution AMOLED display remains more than capable of rendering sharp, legible maps and media controls on the road.

The challenge, however, lies in how to configure such a setup efficiently. A spare phone can technically be operated as a standalone unit running its own navigation apps, but doing so introduces significant friction. It requires duplicating applications, downloading offline maps, and securing a separate source of internet access—either through an expensive dedicated SIM card or by constantly relying on a mobile hotspot from a primary device.

A far more elegant approach avoids these complications by leaning on a specialized Android Auto receiver application. By installing a lightweight projection client onto the older Samsung device, it can function purely as a wireless extension of the user’s main smartphone.

My main phone does most of the work

Under this configuration, the primary smartphone handles all the heavy lifting. It executes the navigation software, processes the music streaming, locks onto GPS satellites for positioning, and maintains an active cellular data connection. Meanwhile, the secondary device in the dashboard acts more like a traditional factory head unit, focusing its processing power primarily on rendering video and capturing touch inputs.

The Galaxy S21 FE possesses far more raw processing muscle than necessary for this task alone. The key software bridging the gap is an application known as Open Headunit. Operating over a local Wi-Fi connection, Open Headunit receives the graphical interface streamed wirelessly from the primary phone and projects it onto the older screen. When a driver taps a playback button or zooms into a map on the dashboard, the secondary phone instantly registers the touch and relays the command back to the primary pocket device.

This architecture eliminates the need for a secondary data plan or duplicate app logins. Saved favorite locations, personalized music playlists, and routine commuting destinations remain synchronized on the device the user already carries everywhere.

Nevertheless, certain hardware realities must be considered when choosing a secondary device for this role. Even though the primary phone shoulders the computational burden, the older display unit must still possess enough performance to smoothly decode incoming video streams without lag. Furthermore, physical attributes such as maximum screen brightness and overall battery health become critical factors—especially when dealing with second-hand hardware. If a display washes out under direct daylight or struggles with thermal management, high processor speeds elsewhere will not compensate for poor visibility on the road.

Setting up the wireless connection

Bringing this configuration to life requires specific software tools and initial pairing steps. Open Headunit supports seamless wireless Android Auto projection, including direct device-to-device links that bypass traditional local network routers. While the application is available on official storefronts for a nominal fee, it is also accessible for free through open-source developer repositories on GitHub.

To establish a stable connection, the receiver app requires permissions to discover nearby hardware and utilize the microphone for voice commands. Concurrently, the primary smartphone must have Android Auto enabled alongside active Wi-Fi, Bluetooth, and mobile data settings.

Within the configuration menu of Open Headunit, users select the native Android Auto mode paired with a direct wireless protocol. This establishes an ad-hoc link between the two phones, sparing the user from manually toggling a mobile hotspot on their primary device every time they enter the vehicle. The primary phone continues utilizing its standard cellular connection for internet traffic, streaming, and GPS data, while the secondary screen mirrors the dashboard interface.

After completing the initial handshake—which requires both devices to remain unlocked during pairing—the system operates reliably. Real-world testing over a typical week-long driving cycle demonstrates that navigation routing, audio playback, touch sensitivity, and voice-activated commands function without noticeable latency. Drivers can secure their primary smartphone in a pocket or bag, and the projection continues uninterrupted on the dashboard. Reconnection upon returning to the vehicle happens automatically, allowing for a seamless transition upon re-entering the car.

Drivers opting for this setup must ensure they use a secure dashboard mount paired with a reliable car charger to maintain power during extended journeys. Long-term exposure to direct sunlight through a windshield can accelerate battery degradation and, in extreme cases involving aging lithium-ion cells, present thermal safety risks that demand careful attention.

The old phone can run Android Auto itself

An alternative approach exists for those who prefer complete isolation between their personal communication device and their vehicle’s dashboard. Open Headunit includes an alternate configuration known as Self Mode, which allows a single device to host both the Android Auto driving interface and the receiver application locally.

In this scenario, the older phone operates as a fully independent car computer. It requires local installation of navigation packages, media apps, and personal account credentials directly on the secondary hardware. While this transforms the old phone into a dedicated automotive console, it reintroduces the connectivity hurdles that make projection-based setups more appealing.

Accessing real-time traffic updates and music streaming in Self Mode requires either a dedicated cellular plan via a separate SIM card or continuous reliance on an external Wi-Fi hotspot, adding recurring monthly costs or manual pairing steps. Additionally, because the older phone must process mapping data and maintain an active screen while charging, thermal management and battery strain become much more prominent concerns. Incoming phone calls and text messages tied to a primary cellular number would also require an alternative routing solution, as the dashboard device operates on a separate local profile.

Despite these drawbacks, Self Mode remains a viable alternative for specific scenarios—such as a shared family vehicle where multiple drivers might use the car without the original owner’s primary smartphone present. For individual use, however, keeping applications and mobile connectivity anchored to the primary pocket device while utilizing an older handset purely as an external display offers a more streamlined, maintenance-free driving experience.