Let me start by saying these little alarms are a steal for the price. At roughly $1 per unit, you're getting decent security without breaking the bank. I've installed them throughout my home - on windows, doors, even some cabinets - and they do their job well.
The installation is dead simple. Just peel off the adhesive backing and stick them in place. The magnets need to be aligned properly (follow those arrows!), but once set up, they trigger reliably when separated. The 90dB alarm is loud enough to startle intruders and alert you without being ear-splitting.
Where these really shine is versatility. I've used them to child-proof cabinets, secure basement windows, and even monitor my garage door. The wireless design means no complicated wiring - just stick and go. They've given me peace of mind knowing I'll be alerted if someone tries to enter through vulnerable points in my home.
Now for the not-so-great parts: The adhesive could be stronger. After a few weeks, I had to reinforce some units with extra double-sided tape. Also worth noting - they don't come with batteries (you'll need AAA), which feels a bit cheap at this price point.
The biggest complaint? They can be temperamental. Sometimes they false alarm for no apparent reason, other times they don't trigger when expected. New batteries help, but it's not a perfect system.
Bottom line: For basic security at an unbeatable price, these get the job done. Just don't expect professional-grade reliability or features.