I want to buy a used car soon. I wonder if would make a cheap alarm system on car insurance?

An alarm system on a used car won’t make your insurance “cheap” but it will probably make it a few dollars lower.

The difference will be on the “comprehensive” coverage line on your policy. It won’t affect your liability coverage, nor the collision coverage. (That’s because the alarm makes the car a little less likely to be stolen, and a stolen car is protected by the comprehensive coverage.)

Depending on the company, and the state you live in, there may be discounts for other related things: An alarm that disables the engine; glass breakage sensor; tracking device (such as lo-jack); VIN etched in the windows; etc.

Make it easy on yourself: Call your current insurance company and ask. (And if you don’t have a current insurer, start calling around and getting quotes.)