Depends on where you are using it (environment), and what price you are willing to accept. Then look for several companies and ask more, and consider it comprehensively. The formaldehyde detectors on Taobao are generally of civilian grade and look good, but the real detection data needs to be verified. The prices on Taobao vary greatly, ranging from hundreds to thousands. If your requirements are high, you should look for one that makes industrial-grade products. For example, Ampal, Neuforth, Cassadine, etc. are all professional gas detection instrument manufacturers with high cost performance.