Sprinkle smoked salt onto a small plate. Rub the rim of a double-old fashioned (or tall) glass with a lime or grapefruit wedge. Dip glass onto a plate of smoked salt. Fill glass with ice.

In a cocktail mixing glass (or pint glass), stir mezcal, grapefruit juice, lime juice and orange bitters.

Pour over prepared glass and top with seltzer water. Garnish with lime and/or grapefruit wedges.