Methane （CH

4

） is an important clean energy source and chemical feedstock. However， due to its colorless， odorless nature and low explosion limit， the leakage of CH

4

during production， transportation， and usage poses significant safety hazards. Therefore， the development of high-performance CH

4

sensors capable of real-time monitoring and early warning is of great practical significance. Conventional metal oxide semiconductor-based CH

4

sensors， such as those employing SnO

2

， ZnO， NiO， and TiO

2

， typically require operating temperatures above 200°C to achieve sufficient sensitivity. Such high-temperature operation leads to high power consumption and restricts their integration with heat-sensitive flexible substrates， limiting their applicability in wearable devices. Consequently， there is an urgent need to develop

CH

4

sensors that can operate at near-room temperature with low power consumption while maintaining high sensitivity， fast response， good stability， and excellent selectivity. To address this challenge， the present study proposes a strategy of constructing an indium oxide （In

2

O

3

）/tin disulfide （SnS

2

） heterojunction followed by decoration with Ag nanoparticles， aiming to achieve superior CH

4

sensing performance at 30°C.In this work， In

2

O

3

/SnS

2

heterojunction nanosheets were first synthesized via a two-step hydrothermal method. In the first step， SnS

2

nanosheets with a regular hexagonal morphology were prepared using SnCl

4

·5H

2

O and thiourea as precursors at 180°C for 12 h. In the second step， In（NO

3

）

3

·4H

2

O was introduced into the SnS

2

suspension with an In/Sn molar ratio of 3：1， followed by hydrothermal treatment at 180°C for 6 h to yield the In

2

O

3

/SnS

2

heterojunction （denoted as IS）. Subsequently， Ag nanoparticles were decorated onto the IS surface via an in-situ deposition method using AgNO

3

and NaOH， followed by thermal treatment at 350°C in air for 1 h. By adjusting the Ag precursor amount， a series of Ag-IS samples with Ag loadings of 0.5， 1， 2， and 3 wt.% were obtained and designated as Ag

0.5

-IS， Ag

1

-IS， Ag

2

-IS， and Ag

3

-IS， respectively. The crystal structure， surface chemical states， and morphology of the as-prepared materials were characterized by X-ray diffraction， X-ray photoelectron spectroscopy， field emission scanning electron microscopy， and energy dispersive spectroscopy elemental mapping. The gas-sensing performance of the fabricated sensors toward CH

4

was systematically evaluated using a JF02F gas sensor testing system at 30°C under a controlled relative humidity of （23±5）% RH. The tested CH

4

concentration ranged from 200 to 2000

 ppm. Key sensing parameters including response value， response/recovery time， dynamic response characteristics， cycling stability， 30 day long-term stability， and selectivity against potential interfering gases （ethanol， methanol， CO， and NH

3

） were comprehensively measured. All sensing tests were repeated on at least three independent parallel devices， and the data are presented as mean ± standard deviation. Furthermore， the anti-humidity performance of the Ag

2

-IS sensor was investigated by controlling the relative humidity in the test chamber from 23% to 75% using the saturated salt solution method. The mechanical stability of the flexible sensor was evaluated by subjecting it to repeated bending cycles at a curvature radius of 20 mm， with the sensing performance measured after 0， 50， 100， and 200 bending cycles. Finally， the sensor with the optimal performance was integrated into a wearable face mask to construct a real-time CH

4

leakage alarm system for proof-of-concept demonstration.The XRD results revealed that the crystal structures of SnS

2

（JCPDS No. 23-0677） and In

2

O

3

（JCPDS No. 06-0416） remained unchanged after Ag decoration， while new diffraction peaks at 38.1°， 44.3°， and 64.5° corresponding to metallic Ag （JCPDS No. 65-2871） confirmed the successful deposition of Ag nanoparticles onto the IS heterojunction surface. XPS analysis further demonstrated that Ag decoration significantly increased the relative content of chemisorbed oxygen species on the material surface， which serve as key active sites for CH

4

sensing reactions. The coexistence of metallic Ag

0

and partially oxidized Ag

＋

was identified from the Ag 3d high-resolution spectrum， suggesting a dual-functional role of Ag： Ag

0

acts as an electron acceptor to modulate the interfacial carrier concentration， while Ag

＋

provides active sites for CH

4

adsorption and activation. FESEM observations showed that the SnS

2

nanosheets exhibited a regular hexagonal morphology with an average diameter of approximately 500 nm， and this two-dimensional structure was well preserved after the growth of In

2

O

3

nanoparticles and subsequent Ag decoration. Ag nanoparticles were uniformly dispersed on the IS nanosheet surface without noticeable agglomeration. EDS elemental mapping confirmed the homogeneous spatial distribution of Sn， In， S， O， and Ag elements throughout the Ag

2

-IS sample.The gas-sensing tests demonstrated that the Ag

2

-IS sensor （with 2 wt.% Ag loading） exhibited the best overall performance at 30°C. The response value of Ag

2

-IS toward 500 ppm CH

4

reached 55.5%， which was substantially higher than those of pure In

2

O

3

， pure SnS

2

， and the undecorated IS heterojunction. The response and recovery times were 27 s and 29 s， respectively， indicating rapid detection capability. A good linear relationship between the response value and CH

4

concentration was obtained in the range of 200-2000 ppm. The sensor exhibited excellent repeatability over multiple response–recovery cycles with negligible signal degradation. In the 30 day long-term stability test， the response value fluctuated within less than 4.7% and showed no obvious attenuation trend， confirming outstanding long-term operational stability. Selectivity tests revealed that the Ag

2

-IS sensor exhibited a markedly higher response toward CH

4

compared with ethanol， methanol， CO， and NH

3

at the same concentration of 200 ppm. Anti-humidity tests showed that although the response value decreased slightly with increasing relative humidity from 23% to 75% RH due to competitive adsorption of water molecules， the sensor maintained a reasonably high response level across the entire humidity range. Mechanical bending tests demonstrated that the sensing performance remained essentially unchanged after 200 bending cycles at a curvature radius of 20 mm

， indicating excellent mechanical flexibility and durability. When integrated into a wearable face mask， the Ag

2

-IS sensor successfully triggered a light-emitting diode alarm upon exposure to 1000 ppm CH

4

， validating its feasibility for practical wearable CH

4

early-warning applications.The superior CH

4

sensing performance of the Ag

2

-IS heterojunction can be attributed to the synergistic effects of several factors. Firstly， the In

2

O

3

/SnS

2

n-n heterojunction promotes interfacial charge separation through the internal electric field， enhancing the modulation of carrier concentration upon gas exposure. Secondly， Ag nanoparticles play a dual catalytic and electronic regulatory role： Ag

0

facilitates electron transfer and modulates the Schottky barrier at the Ag-In

2

O

3

interface， while Ag

＋

provides active sites for CH

4

adsorption and lowers the activation energy for C-H bond cleavage. Thirdly， the increased chemisorbed oxygen content induced by Ag decoration supplies abundant reactive oxygen species for CH

4

oxidation. Finally， the two-dimensional nanosheet morphology offers a large specific surface area and abundant active sites for gas adsorption and surface reactions. This study demonstrates that the combination of heterojunction construction and noble metal decoration is an effective strategy for developing high-performance CH

4

sensors operating at near-room temperature， and the fabricated Ag-In

2

O

3

/SnS

2

heterojunction holds great promise for applications in low-power， flexible， and wearable CH

4

detection devices for personal safety protection.