## 4 Results
### Criteria for Comparing the Relevant Characteristics
\begin{table}
\begin{tabular}{c c c c} \hline
**Criteria** & **[PERSON] et al. [68]** & **[PERSON] et al. [69; 70; 71; 72]** & **[PERSON] et al. [73]** \\ \hline \multicolumn{4}{c}{**System-on-Chip (SoCr)**} \\ \hline Microcontroller (Single-Board Computer) & WeMoes Mini DI ESP8266 Wi-Fi & ESP8266 (Essressif Systems) & Arduino mkr \\ \hline \multirow{2}{*}{Based CPU} & Tensilica Xensens Diamond 32-bit & Tensilica L106 32-bit RISC processor & \multirow{2}{*}{ARM Cortex-M0 + CPU (48 MHz)} \\  & (80/160 MHz) & (160 MHz) & \\ \hline Wireless module & IEEE 802.11 b/g/n transceiver & ESP-WROOM-32 & Arduino Mkr Wi-Fi 2020 \\ \hline \multicolumn{4}{c}{**Communication technologies:**} \\ \hline Gateway & - & LoRaWAN: Microchip RN 2483 & - \\ \hline Wireless Protocols (available) & Wi-Fi (IEEE 802.11 b/g/n) & Wi-Fi (IEEE 802.11 b/g/n) and LoRaWAN & Sigfox and Wi-Fi (IEEE 802.11 b/g/n) \\ \hline Hardware communication protocol & - & UART/ADC/OneWire/\({}^{2}\)C & UART/I\({}^{2}\)C \\ \hline \multicolumn{4}{c}{**Wireless Communications (used):**} & **Wi-Fi (licence-free 2.4 GHz and 5 GHz)** & **LoRaWAN (licence-free sub-1 GHz)** & **Sigfox (licence-free sub-1 GHz)** \\ \hline Center frequency & 24/50 GHz & 868 MHz & 868.130 MHz \\ \hline Bandwidth & 20/40 MHz & 125 kHz & 200 kHz (ultra-narrow) \\ \hline Data rate (bits/s) & -500 Mbps & 250 bps–50 kbps & 100 \\ \hline \multicolumn{4}{c}{Effective isotropic radiated power} & - & +14 dBm (receiver sensitivity: 16 dBm \\  & -146 dBm) & \\ \hline Constraints & Max. payload 64 KB & Limited message sizes (230 bytes & 140 messages/day (ETSI regulations) \\  & & at most) & \\ \hline \multicolumn{4}{c}{**Radon gas sensor:**} \\ \hline Radon sensor & Safety Siren Pro Series 3 & Radon FTLab RD200M & Radon FTLab RD200M \\ \hline Academic prototype/Commercial sensor & Commercial sensor (for & Academic prototype (for \\ prototype/Commercial sensor & indoor dosimetry) & indoor dosimetry) \\ \hline Radon detection technique & Photodiode detection for & Pulsed Ion chamber & Pulsed Ion chamber \\  & alpha particles & & \\ \hline First data out & - & \textless{}60 min & \textless{}60 min \\ \hline Data interval & Update’s readings every hour (mean, & 10 min update (60 min & 10 min update (60 min \\  & max/min) & moving average) & moving average) \\ \hline Sensitivity & - & 0.81 cph \(\pm\) 1 Bq/m\({}^{3}\) & 0.81 cph at 1 Bq/m\({}^{3}\) \\ \hline Operating range & 0–40 \({}^{\circ}\)C, RH + 80\% & 10–40 \({}^{\circ}\)C, RH + 80\% & 10–40 \({}^{\circ}\)C, RH + 80\% \\ \hline Measurement range (Bq/m\({}^{3}\)) & 0–37,000 & 7–3700 & 7–3700 \\ \hline Typical accuracy (precision) & \(\pm\)10\% & \(<\)10\% @ 370 Bq/m\({}^{3}\) & \(<\)\(\pm\)10\% at 370 Bq/m\({}^{3}\) \\ \hline Guaranteed accuracy & \(\pm\)20\% or 37 Bq/m\({}^{3}\) the highest & - & - \\  & of both/ & - & \\ \hline Display & LED Display (four-digit & None & OLED Display \\  & seven-segment-based) & & \\ \hline Other information & Discontinued & Built-in vibration sensor to & Built-in vibration sensor to \\  & & prevent errors & prevent errors \\ \hline \multicolumn{4}{c}{**Environmental sensors included:**} \\ \hline Gas sensor (IAQ) & - & MQ-135 (indoor CO\({}_{2}\) variations) & CCS811 (TVOC, eCO\({}_{2}\), MOX) \\ \hline Relative humidity/temperature: & - & Aosong DHETIN (repeatibility: \(\pm\)1\%, & BME280 \\  & & \(\pm\)2\({}^{\circ}\)C) & \\ \hline Bareometric pressure & - & NXP MPL315A2 & - \\ \hline \multicolumn{4}{c}{**Back-end web architecture:**} \\ \hline Open-source virtualization platform & - & - & Proxmox VE (KVM hypervisor + LXC \\  & & - & Containers + Storage + Networking \\ \hline Programming tool for wiring devices & - & - & Node-RED (browser-based editor) \\  & and API & & GeoServer & - \\ \hline Geographic Information System (GIS) & - & GeoServer & - \\ \hline Threshold for issuing alerts & 200 Bq/m\({}^{3}\) & 300 Bq/m\({}^{3}\) & 300 Bq/m\({}^{3}\) \\  & & & MQTT & MQTT and SMTP (email) \\ \hline Messaging protocols & & & \\ \hline Security protocols & None & 128 bits AES keys (AppKey, AppKeyKey & \\  & and NwlxSkey) + SSL + MQTT Secure & HTIPS (SSL with ACME protocol) \\ \hline NFC device to secure credentials & - & - & NXP NTAG PC plus \\  & & & \\ \hline \multicolumn{4}{c}{**Prototype dimensions, estimated power consumption, and price:**} \\ \hline Dimensions & 12.0 \(\times\) 7.9 \(\times\) 5.3 cm & 10.0 \(\times\) 10.0 \(\times\) 15.0 cm & 15 \(\times\) 15 \(\times\) 30 cm \\ \hline Overall power consumption (Wh) & n/a & 1.65 & n/a \\ \hline Overall price of the system & n/a & n/a & n/a \\ \hline \end{tabular}
\end{table}