They are new, expired so they are being sold as a collectable. The cards show their age a bit but they are unopened.
eBay
2in1 20W UV+White light High Power Flashlight 365nm USB Charging Blacklight Money Ore Pet Stains Leakage Marker Detector lamp
Aliexpress UK
(The specific item pictured, including all components shown in the photos, is what you will receive. Model: 8217. 1.75 lbs). Condition: C4 - Used Good. Item shows signs of wear but is fully functional.
eBay
F999R Microphone Water Leakage Listens Tester Tools Water Leak Detection Repair Pipe Leak Detector
Aliexpress UK
This Micronta 22-2001 Microwave Leakage Detector is a reliable and efficient tool for detecting any radiation leakage in your microwave. The device, purchased in the 1980s from Tandy Radio Shack, comes with a receipt to authenticate its authenticity. The item is in a new condition with no signs of use. But this is for collectors only if used I hold no responsibility as it was made nearly 45 years ago.
eBay
Tuya Wifi Natural Gas Leakage Detector Sensor Smart Alarm Gas Fire Security Digital LED Temperature Display for Home Kitchen
Aliexpress UK
Latnex MW-A3G: Microwave Leakage Detector Some minor wear to the outer box. Comes with battery and instructions
eBay
BSIDE Leakage Voltage Detector Tester AC Creepage Electric Pen Non-contact Circuit Continuity 0~300V With Backlight Lighting
Aliexpress UK
MLD-2000 Microwave Leakage Detector & Soft Case Not tested Sold as seen No return accepted
eBay
Smart ZigBee Gas Leakage Detector Combustible Sensor Tuya Smart Home Security Alarm System Smart Life Tuya App Remote Control
Aliexpress UK
The Di-LOG DL7206 microwave leakage detector quickly and easily checks your microwave/microwave leakage and has the following features. - Alarm sounds and red LED light flashes when microwave leakage is detected.
eBay
Home Alarm Water Leakage Alarm Independent 90DB WIFI Water Leak Sensor Detector Flood Alert Overflow work With Tuya APP
Aliexpress UK
RS PRO MICROWAVE LEAKAGE DETECTOR. RS PRO MICROWAVE LEAKAGE DETECTOR WITH CASE, MANUAL AND BATTERY. SCREEN PROTECTOR STILL IN PLACE. SEEN LITTLE IF ANY USE. IN NEAR MINT CONDITION OTHER THAN MARK TO REAR OF CASING AS SHOWN.
eBay
Tuya Zigbee 2mqtt Water Immersion Sensor Smart Life Leakage Sensor Water Linkage Alarm App Remote Monitoring Water Leak Detector
Aliexpress UK
TheMartindale TEK500 Microwave Leakage Detector Kit is a professional tool designed to check for microwave radiation leakage, helping ensure appliances are safe to use. Martindale TEK500 Microwave Leakage Detector.
eBay
Water Leakage Alarm Detector with EU Power Adapter and 4pcs Wired Water Sensor Cable
Aliexpress UK