| Hardware and OS | Karbonn A21 | Oppo A3s |
| Operating system | Android 4.0 (Ice Cream Sandwich) | Android 8.1 (Oreo); ColorOS 5.1 |
| Processor | Dual-core 1.2 GHz | Octa-core 1.8 GHz Cortex-A53 |
| Internal memory | 4 GB, 512 MB RAM | 16 GB, 2 GB RAM |
| Chipset | | Qualcomm SDM450 Snapdragon 450 (14 nm) |
| External memory | microSD, up to 32 GB (dedicated slot) | microSD, up to 256 GB (dedicated slot) |
| GPU | | Adreno 506 |
| Display | Karbonn A21 | Oppo A3s |
| Type | TFT | IPS LCD |
| Size | 4.5" inc | 6.2" inc |
| Resolution | 480 x 800 px | 720 x 1520 px |
| Touchscreen | capacitive touchscreen | capacitive touchscreen |
| Display area | 57.6 cm2 | 95.9 cm2 |
| Display aspect ratio | 5:3 (height:width) | 19:9 (height:width) |
| Pixel Density | 207 PPI | 271 PPI |
| Screen-to-Body Ratio | | 81.2% |
| Colors | 256K | 16M |
| Connectivity | Karbonn A21 | Oppo A3s |
| 2G Network | GSM 900 / 1800 / 1900 - SIM 1 & SIM 2 | GSM 850 / 900 / 1800 / 1900 - SIM 1 & SIM 2 |
| Wi-Fi | Wi-Fi 802.11 b/g/n | Wi-Fi 802.11 b/g/n, WiFi Direct, hotspot |
| Network | GSM / HSPA | GSM / HSPA / LTE |
| SIM card | Dual SIM (Mini-SIM) | Dual SIM (Nano-SIM, dual stand-by) |
| Bluetooth | 2.1, A2DP | 4.2, A2DP, LE |
| 3G Network | | HSDPA 850 / 900 / 2100 |
| Edge | Yes | Yes |
| 4G Network | | LTE |
| GPRS | Yes | Yes |
| GPS | Yes, with A-GPS | Yes, with A-GPS |
| Speed | HSPA 7.2/0.384 Mbps | HSPA 42.2/5.76 Mbps, LTE-A (2CA) Cat6 300/50 Mbps |
| USB | microUSB 2.0 | microUSB 2.0, USB On-The-Go |
| Camera | Karbonn A21 | Oppo A3s |
| Main camera | 5 MP, Single | 13 MP, Dual |
| Specs | 5 MP, AF | 13 MP, f/2.2, AF
-2 MP, f/2.4, depth sensor |
| Features | LED flash | LED flash, HDR, panorama |
| Video | Yes | 1080p@30fps |
| Selfie camera | 1.3 MP, Single | 8 MP, Single |
| Multimedia | Karbonn A21 | Oppo A3s |
| 3.5 mm Jack | Yes | Yes |
| Radio | No | FM radio |
| Design | Karbonn A21 | Oppo A3s |
| Colors | Pearl White | Red, Dark Purple |
| Dimensions | | 156.2 x 75.6 x 8.2 mm |
| Weight | | 168 g |
| Battery | Karbonn A21 | Oppo A3s |
| Battery capacity | 1800 mAh, Removable Li-Ion | 4230 mAh, Non-removable Li-Ion |
| Battery life | Stand by time- Up to 200 h
Talking time- Up to 5 h
| |
| Other | Karbonn A21 | Oppo A3s |
| SAR | SAR EU - 0.44 W/kg (head) | |
| Release date | 2012 | 2018, July |
| Sensors | Accelerometer, proximity | Accelerometer, proximity, compass |
