Travelers feeling the need for an emergency alarm to summon help or scare away threatening animals or humans have used everything from compressed-air horns to loud metal whistles. For really piercing protection, consider the powerful little battery-powered BASU eAlarm. Think of it as a sound grenade that sends out a deafening siren when you pull out the pin inserted in one end of the device. A plastic loop extending from the pin provides a firm grip and secures the eAlarm to a key ring, belt loop, or any strap via an included metal carabiner. The device's cheery color choices and diminutive size (2.79-by-1.22-by-.51 inches) belie its fierceness. Yank out the pin, and an ear-splitting 120-decibel siren will accost anyone or anything in your path - and likely leave your own eardrums ringing even after you have silenced the alarm by plugging the pin back into its slot.
But there's an even more aggressive eAlarm - the 130-decibel, slightly longer eAlarm Plus. The extra length accommodates an integrated hook at the end opposite the pin, adding the option of a tripwire alarm. Secure the hook (rope not included) to a stationary object - say, a metal fence post or tree trunk or bike rack - and clasp the carabiner at the armed end to your backpack or luggage handle or bike frame. Anyone who tugs on your stuff will get an instant earful - and alert you and everybody else in the area. The trip alarm can't prevent theft and is no substitute for a high-grade antitheft lock system to secure anything you must leave unattended. But the sudden prolonged scream might provide enough shock effect to slow the grabber and/or trigger pursuit.
Both e-Alarm models are powered by two preinstalled CR1632 batteries. They provide 30 minutes total siren power. You decide whether the situation calls for a brief blast or a long tortuous shriek. The sound and cadence of the siren will begin to weaken as the battery runs low, a signal to replace the device. Although it's possible to pry open an eAlarm with a sharp knife and replace the batteries, loosening the casing will free the pin, triggering the alarm (ouch, I tried it). The manufacturer strongly discourages tinkering, and my throbbing eardrums agree.