The Apple Watch Series 4 brought a significantly larger display and groundbreaking ECG capability to Apple's health monitoring ecosystem for comprehensive wellness tracking. Choosing a refurbished smartwatch gives you access to advanced health features while making an environmentally conscious decision. Find the watch that revolutionized wearable health technology with expanded screen space and FDA-cleared heart monitoring.
What are the key features of the Apple Watch Series 4?
- Larger Retina display: over 30% more screen area than Series 3 with 40mm and 44mm case sizes
- ECG capability: FDA-cleared electrocardiogram app for on-demand heart rhythm analysis
- Irregular heart rhythm notifications: passive monitoring alerts you to potential atrial fibrillation
- Fall detection: automatically detects hard falls and calls emergency services if you're unresponsive
- Enhanced heart rate sensor: optical and electrical sensors provide more accurate readings and enable ECG
- S4 dual-core processor: twice as fast as Series 3 for smoother performance
- Digital Crown with haptic feedback: tactile clicks when scrolling enhance the navigation experience
- Built-in GPS: accurate outdoor tracking for running, cycling, and walking without your phone
- Water resistant to 50 meters: swim-proof design for pool and open water activities
- Louder speaker: 50% louder for clearer calls and alerts
- iPhone compatibility: works with iPhone 6s or later running iOS 13 or higher
What are the differences between a refurbished and a used Apple Watch Series 4?
A used Apple Watch Series 4 is resold without professional inspection or warranty. The ECG sensors and electrical heart monitoring can degrade from wear, affecting the accuracy of heart rhythm analysis. Water resistance seals may be compromised. A refurbished Apple Watch Series 4 from Back Market has been thoroughly tested by trusted refurbishers following our Quality Charter.
Each watch undergoes comprehensive inspection of ECG functionality, electrical and optical heart rate sensors, fall detection accelerometer and gyroscope, GPS accuracy, Digital Crown haptic feedback, speaker and microphone quality, display condition, battery health, water resistance seals, and charging capability. Every device comes with a minimum 1-year warranty and 30-day returns. You get pioneering health monitoring technology without the premium new price, while reducing electronic waste.
Who is the Apple Watch Series 4 best for?
The Apple Watch Series 4 serves several types of users particularly well:
- People monitoring heart health: ECG capability and irregular rhythm notifications help track cardiovascular wellness
- Older users or those with medical conditions: fall detection provides safety monitoring during daily activities
- iPhone users upgrading from Series 3 or earlier: significantly larger display and ECG offer meaningful improvements
- Fitness enthusiasts: accurate GPS, comprehensive workout modes, and heart rate tracking support active lifestyles
- Budget-conscious buyers wanting health features: Series 4 offers ECG at lower refurbished prices than Series 5, 6, 7, or 8
- Users wanting expanded screen space: 30%+ larger display makes text, notifications, and apps much easier to read
Apple Watch Series 4 vs Series 5 and newer: which should you choose?
The Apple Watch Series 5 added Always-On Display, built-in compass, and international emergency calling over the Series 4. All other features—ECG, fall detection, heart rate monitoring, case sizes, and water resistance—remain essentially identical. The S5 processor performs similarly to the S4 for daily tasks. If Always-On Display matters (seeing the time without raising your wrist), choose Series 5. If you're fine with the screen sleeping when your wrist is down, Series 4 offers the same health tracking at better refurbished prices.
The Apple Watch Series 6 added blood oxygen monitoring and an always-on altimeter over the Series 4. The S6 processor is faster, and the display is brighter outdoors. Series 6 charges slightly faster. Both share ECG, fall detection, and the same larger display size introduced in Series 4. Choose Series 6 if you want SpO2 tracking for respiratory wellness or altitude monitoring. Choose Series 4 if those sensors don't matter and you want to save money.
Series 7 and 8 brought an even larger display (nearly 20% bigger than Series 4), faster charging, crack-resistant crystal, and dust resistance. Series 8 added temperature sensing and crash detection. These are meaningful upgrades, but the Series 4 still delivers comprehensive health monitoring including ECG and fall detection at the lowest price point among models with these features.
Choose Series 4 if you want ECG capability, fall detection, and the expanded display at the most accessible refurbished price. It remains a capable health and fitness tracker. Choose newer models if you want Always-On Display (Series 5+), blood oxygen monitoring (Series 6+), or the absolute largest screen with latest features (Series 7+).
Buy a refurbished Apple Watch Series 4 at the best price on Back Market
Back Market offers refurbished Apple Watch Series 4 models at competitive prices with pioneering health monitoring features. Each watch is:
- Tested by trusted refurbishers: ECG functionality, fall detection, heart rate sensors, GPS, and all health features verified working
- Backed by warranty: minimum 1-year coverage protects your investment
- Returnable for 30 days: test it through daily use and workouts to ensure it meets your health tracking needs
- Better for the environment: choosing refurbished reduces e-waste and extends product lifecycles
Browse different cosmetic grades from Premium (like-new condition) to Fair (fully functional with minor cosmetic wear). Choose between 40mm and 44mm sizes, GPS or GPS + Cellular connectivity, and various case materials including aluminum, stainless steel, and titanium. The Series 4 represents excellent value for users wanting ECG and advanced health monitoring without paying for the latest generation.
How does the ECG feature work on Apple Watch Series 4?
The ECG app uses electrical heart sensors built into the back crystal and Digital Crown. Place your finger on the crown while wearing the watch for 30 seconds, and the sensors measure electrical signals across your heart. The app classifies the reading as sinus rhythm (normal), atrial fibrillation (AFib), low or high heart rate, or inconclusive. Results save to the Health app and can be exported as a PDF to share with your doctor. The ECG feature is FDA-cleared but isn't a diagnostic medical device—it helps identify potential irregular heart rhythms worth medical consultation. The Series 4 was the first consumer device to offer FDA-cleared ECG capability.
What is fall detection and how reliable is it?
Fall detection uses advanced motion sensors (accelerometer and gyroscope) to identify when you've taken a hard fall. If the watch detects a fall, it taps your wrist, sounds an alarm, and displays an alert asking if you're okay. If you're moving, it assumes you're fine. If you remain motionless for about one minute, it automatically calls emergency services and sends a message with your location to your emergency contacts. You can enable fall detection for all ages or just ages 65 and older in settings. It's not perfect—false positives and missed falls can occur—but it provides valuable safety backup, especially for older users or those with medical conditions.
How much bigger is the Apple Watch Series 4 display?
The Series 4 display is over 30% larger than the Series 3 while keeping similar overall case dimensions. Apple achieved this by significantly reducing the bezels around the screen and rounding the display corners. The 40mm Series 4 has more screen area than the 42mm Series 3. Text is noticeably larger and easier to read. Complications show more information. The keyboard for typing messages works much better with the extra space. The display expansion was one of the Series 4's most significant improvements and remains valuable—the screen feels spacious compared to Series 3 and earlier models.
Does the Apple Watch Series 4 have Always-On Display?
No, the Series 4 doesn't include Always-On Display. You need to raise your wrist, tap the screen, or press the Digital Crown to wake the display and see the time. Always-On Display was introduced with Series 5. The Series 4 screen turns off when your wrist is down to conserve battery. Many users adapt to this and don't miss Always-On Display, while others find it inconvenient compared to traditional watches. If seeing the time without wrist movement matters, consider Series 5 or newer. If you're fine with raise-to-wake, the Series 4 works perfectly well.
What's the battery life on the Apple Watch Series 4?
Expect up to 18 hours of typical use with standard settings including notifications, occasional workouts, heart rate monitoring, and ECG checks. This matches Apple's battery estimate for most Apple Watch models. During continuous GPS tracking for running or cycling, expect roughly 5-6 hours before needing to recharge. The watch charges fully in about 2-2.5 hours using the included magnetic charging cable. Most users charge nightly and get through a full day comfortably with typical use. Battery capacity may be slightly reduced on refurbished units depending on age and usage history.
Can I track sleep with the Apple Watch Series 4?
Sleep tracking became available on Series 4 through watchOS updates. The watch monitors sleep duration, sleep stages (REM, Core, Deep), heart rate, and respiratory rate during sleep. Sleep data syncs to the Health app. The watch needs at least 30% battery to track sleep through the night, so you'll need to charge at another time—many users charge while getting ready in the morning or during the evening before bed. The Series 4's sleep tracking experience and accuracy are similar to newer models, though it lacks features like temperature sensing found on Series 8.
Does the Apple Watch Series 4 have blood oxygen monitoring?
No, the Series 4 doesn't include blood oxygen (SpO2) monitoring. This feature was introduced with the Apple Watch Series 6. The Series 4 monitors heart rate continuously and includes ECG capability, but it can't measure oxygen saturation levels in your blood. If blood oxygen monitoring matters for altitude training, sleep tracking, or respiratory health monitoring, consider Series 6 or newer models. For most users focused on fitness tracking and general heart health, the Series 4's sensor suite remains comprehensive.
Is the Apple Watch Series 4 still supported by Apple in 2026?
The Apple Watch Series 4 (released in 2018) is approaching the end of official watchOS support. Apple typically supports Apple Watch models for 5-7 years with software updates. The Series 4 may not receive the latest watchOS versions, meaning you'll miss new features and eventually security updates. However, the watch continues to function with its current software for fitness tracking, ECG, fall detection, notifications, and core Apple Watch features. If you want guaranteed long-term software support, consider newer models like Series 8 or 9. The Series 4 works well for current needs but has limited future update potential.