The police should never be called on a whim. In most cases, it's best to resolve issues with neighbors the neighborly way: without threats or police cars.
That said, there are certainly cases when efforts at polite exchange fail. Here are four situations in which you should seriously consider calling the police about problems in the neighborhood.
Your neighbors are loud. Unusually loud. They party late into the night without any regard for their surroundings. Look up the noise ordinances in your locality so that you are sure you know what exactly is allowed and what constitutes too much.
First, try talking. Next, leave a written warning. If that doesn't help, it may be time to bring in the authorities. Ideally, you will make the call when the neighbors are home and disturbing the peace. When you call the police, do let them know you tried to resolve the problem on your own and point out any patterns you have noticed.
This is slightly different than a general noise problem. If your neighbors fight with each other a lot and you can hear it and it sounds scary, there might be a problem -- maybe even a safety issue.
People all have different notions of passion, so it's possible that what seems wild to you is just a regular dispute for the couple next door. But if you really have reason to believe that someone is at risk, pick up the phone. Let the police know that you suspect domestic violence.
3. Child Abuse
Just as above, if you suspect your neighbor's child or children are in danger, call the police. Do keep in mind that accusations of abuse are extremely serious and have dramatic consequences in families, even when the claim is unfounded. So, calling the police for this reason is an extremely serious move. But if you truly suspect child abuse, make it.
4. Plethora of Pets
Localities have ordinances that dictate how many animals a person can have and which types. Even if you are far out in the country or deep in the forest, far from the view of any authorities, there are still rules. Look up your local rules and find out what is allowed.
If your neighbor has, say, dozens of cats in an apartment that is probably not okay. Sometimes it's not a question of how many animals but what type. You might try speaking to your neighbor directly about the horse in the backyard or the goats in the garage, but people love their pets.
Call the police if there is an immediate emergency and you don't believe you can speak directly to the neighbor. Unless there is an immediate emergency or danger, the police will likely refer the matter to animal control.
5. Drug Activity
Drug activity can lead to serious public safety or health issues. For example, even a small-scale meth lab in your neighborhood can have long-lasting health consequences. If you consistently notice your neighbors engaging in questionable deals or if you witness obvious usage of illegal drugs, you should alert the authorities.