## 2 Classification Based on Application Time
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Example** & **Type** & **Application Time** & **Theory** & **Height of Application** \\ \hline Snake Eye Life detector & Life detector & 0–72 h & Intercom probe, video probe, and infrared thermal imaging probe & Ground \\ \hline LEADER Hasty & Life detector & 0–72 h & It incorporates vibration signal listening, video searches, and calls to trapped people & Ground \\ \hline Airborne radar-photoelectric composite life-detection system & Life detector & 0–72 h & Two-dimensional radar and visible/infrared cameras & Low altitude \\ \hline Native safety radar vibration compound life detector & Life detector & 0–72 h & Intrinsically safe two-dimensional radar is combined with intrinsically safe wireless micro vibration sensor & Ground \\ \hline Prototype of portable locator employing chemical analysis & Life detector & 0–72 h & Infrared (IR) camera and different gas sensors & Ground \\ \hline  & & & Using hammer strike, electric spark, or explosion as the source, it is aroused by observing and recording the travel time of seismic wave and detecting the buried depth, shape, and distribution law of different elastic stratum interface, so as to solve the problem of engineering and resource geophysical exploration and explore depths from several meters to hundreds of meters & Underground \\ \hline P-alert & Earthquake early warning & Long period & Earthquake P-wave sensor, in addition to the traditional S-wave detection function, but also embedded in the earthquake rapid report technology, can detect P waves and determine a catastrophic earthquake within 3 s. & Underground \\ \hline Alpha GUARD & Earthquake early warning & Long period & Seismic precursor analysis using atmospheric radon anomaly. & Ground \\ \hline CG-5 Gravimeter & Seismic prospecting & Long period & Studies the physical phenomena of gravity changes on the Earth’s surface and in the space around it. & Ground \\ \hline  & & & The acoustic sensor detects the external signal in the optical fiber. By extracting and demodulating the interference signal of sound vibration at different times, the quantitative measurement of external physical quantity can be realized. & Underground \\ \hline Radio-Frequency Identification (RFID) & Communication support & 0–72 h for saving lives and after 72 h for other usages & RFID is a generic term for technologies that use radio waves to automatically identify people or objects. & Ground \\ \hline  & & & A two-way radio is a radio that can both transmit and receive radio waves (a transceiver), unlike a broadcast receiver which only receives content. It is an audio (sound) transceiver, a ground & Above/below ground \\ \hline Two-way radio system & Communication support & Provide the possibility of communication after an earthquake & A two-way radio is a radio that can both transmit and receive radio waves (a transceiver), unlike a broadcast receiver which only receives content. It is an audio (sound) transceiver, a transmitter and receiver in one unit, used for bidirectional person-to-person voice communication with other users with similar radios. & Ground \\ \hline  & & & Satellite communication is the communication between radio communication stations on Earth (including the ground and the lower atmosphere) using satellites as a medium. & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Modern sensors for earthquake monitoring, early warning, search, and rescue.