There are many reasons why a Beagle will bark, however one of the most common is a triggered disturbance.
With disturbance barking, a certain noise is picked up a dog and it causes some type of aggravation or frustration. For this example, we will use the element of a siren (car alarms, fire trucks and so forth). Since a dog's hearing is so heightened, a Beagle can quickly feel severe aggravation and unrest when there is a sudden, high pitched noise.
Envision if without warning, someone blew a whistle directly into your ear and continued doing it for a while! This is how your Beagle most likely feels when hear a siren.
If a siren is just a very occasional event, perhaps 1 time per month, you can use simply calming techniques.
1) If you are outside, bring your dog inside. Whether outside or inside, do not scold your Beagle. This reaction is not due to "bad" behavior. Reassure your dog that everything is alright. Talk in a matter-of-fact voice and gently pat him. Your tone of voice and your actions will be your dog’s cue to know if he or she should be “on alert”.
If you remain very calm and act as if all is fine, your dog will learn to mimic you. If you run around closing windows, covering your dog’s ears, etc…this is signaling to your dog that something is indeed “wrong”, thus causing them to bark even more.
2) If you live in an area that is very noisy with car alarms and sirens always going off, you may wish to attempt to train your dog to cope by desensitizing him or her. This is done by slowly exposing the dog to a noise until he learns that hearing it is not reason for concern. For some Beagles, this can work amazingly well and for others it will at least allow the dog to calm down a bit.
You would obtain a small siren. We have found that using a smoke alarm works well. Duct tape is put over the siren where the noise emits. Use as much as you need so that the end result is that the sound is 1/5 of the normal noise volume when you press the button. Test this before you begin. This training will not end with the maximum noise being emitted since a noise that loud can be quite painful. A certain amount of duct tape will always be used.
You would sit down with your dog and press the alarm. The tone of your voice and your actions must show your Beagle that there is no reason to be on high alert. If the dog responds well to the low level siren, you should reward him or her with tons of praise and treat.
Work with your Beagle each day. Slowly raise the noise level every 2 weeks by taking away a layer of the tape. As time goes by, be in a different room and do not allow your dog to know when you will be implementing the training.
NOTE: Do not have the siren at full noise capacity and hold it up to your Beagle's ears as this could cause injury to the ear drum. Once you have worked your way up to turning on the siren at unexpected times, your Beagle will have become adjusted.