a building, a grenade may be lobbed for greater distance or accuracy. Throwing a grenade upstairs is dangerous, due to the risk of it falling back down; it is much safer to throw a grenade downstairs, so it is safer to capture a building from the top, rather than the bottom. Grenades generally explode near the floor, causing spalling downwards towards lower floors. Alerts The preferred technique in the US forces when attacking is to show the grenade to nearby friendly forces, receiving a visual acknowledgment, to avoid alerting the enemy. Alternatively, a voice alert can be given immediately after throwing the grenade, shouting "frag out" (for "fragmentation grenade outgoing"); this reduces or eliminates the element of surprise. Conversely, on identifying an incoming enemy grenade, friendly forces shout "grenade". Booby traps Grenades have often been used in the field to construct booby traps, using some action of the intended target (such as opening a door or starting a car) to trigger the grenade. These grenade-based booby traps are simple to construct in the field as long as instant fuzes are available; a delay in detonation can allow the intended target to take cover. The most basic technique involves wedging a grenade in a tight spot so the safety lever does not leave the grenade when the pin is pulled. A string is then tied from the head assembly to another stationary object. When a soldier steps on the string, the grenade is pulled out of the narrow passageway, the safety lever is released, and the grenade detonates. Abandoned booby traps and discarded grenades contribute to the problem of unexploded ordnance (UXO). The use of target triggered grenades and AP mines is banned to the signatories of the Ottawa Treaty and may be treated as a war crime wherever it is ratified. Many countries, including India, the People's Republic of China, Russia, and the United States, have not signed the treaty citing self-defense needs. Alternative uses Grenades have also been made to release smoke, tear gas and other gases, as well as illumination. Stun grenades are often used to disorient people during entry into a room, especially where hostages or non-combatants may be present. Some grenades are designed to be thrown longer distances. The German "potato-masher" grenade had a long wooden handle that extended its range by fifty percent. The potato-masher was fired by a friction igniter in the head, activated by a pull string threaded through the hollow handle. Immediately before throwing the grenade, the soldier pulled a small porcelain ball at the end of a string attached to the friction igniter. This started the time fuze, which fired the detonator after a delay. The potato-masher is often incorrectly thought to have had an impact fuze. It did not, but the superficially similar British stick grenade design of 1908 did. Concussion grenades can also be used as general explosives, for instance for demolition. Cultural impact Stylized pictures of early grenades, emitting a flame, are used as ornaments on military uniforms, particularly in Britain, France (esp. French Gendarmerie and the French Army), and Italy (Carabinieri). Fusilier regiments in the British and Commonwealth tradition (e.g., the Princess Louise Fusiliers, Canadian Army) wear a cap-badge depicting flaming grenade, reflecting their historic use of grenades in the assault. The British Grenadier Guards took their name and cap badge of a burning grenade from repelling an attack of French Grenadiers at Waterloo. The Spanish artillery arm uses a flaming grenade as its badge. The flag of the Russian Ground Forces also bears a flaming grenade device. Ukrainian mechanized infantry and engineers use a flaming grenade